The Ramayana vs The MahaBharta

Both these holy books offer different understanding and both of them talk about Krishna. Why did Krishna came up with Mahabharta ( As well as The Gita ) ?. Were there somethings left out or mistaken in The Ramayana ?

Srimad Bhagavatam Canto 1, Ch. 4 text 19

"He saw that the sacrifices mentioned in the Vedas were means by which the people's occupations could be purified. And to simplify the process he divided the one Veda into four, in order to expand them among men."

Purport
"Formerly there was only the Veda of the name Yajur, and the four divisions of sacrifice were there specifically mentioned. But to make them more easily performable, the Veda was divided into four divisions of sacrifice, just to purify the occupational service of the four orders. Above the four Vedas, namely Rg, Yajur, Sama, and Atharva, there are the Puranas, the Mahabharata, Samhitas, etc., which are known as the fifth Veda. Sri Vyasadeva and his many disciples were all historical personalities, and they were very kind and sympathetic toward the fallen souls of this age of Kali. As such, the Puranas and Mahabharata were made from related historical facts which explained the teaching of the four Vedas. There is no point in doubting the authority of the Puranas and Mahabharata as parts and parcels of the Vedas. Acording to Srila Jiva Gosvami, that is the way ascertaining the respective values of the revealed scriptures. "

Srimad Bhagavatam Canto 1, Ch. 3 text 21

"Thereafter, in the seventeenth incarnation of Godhead, Sri Vyasadeva appeared in the womb of Satyavati through Parasara Muni, and he divided the one Veda into several branches and sub-branches, seeing that the people in general were less intelligent."

Purport
"Originally the Veda is one. But Srila Vyasadeva divided the original Veda into four, namely Sama, Yajur, Rg, Atharva, and then again they were explained in different branches like the Puranas and the Mahabharata. Vedic language and the subject matter are very difficult for ordinary men. They are understood by the highly intelligent and self-realized brahmanas. But the present age of Kali is full of ignorant men. Even those who are born by a brahmana father are, in the present age, no better than the sudras or the women. The twice-born men, namely the brahmanas, ksatriyas and vaisyas, are expected to undergo a cultural purificatory process known as samskaras, but because of the bad influence of the present-age the so-called members of the brahmana and other high-order families are no longer highly cultured. They are called the dvija-bandhus, or friends and family members of the twice-born. But these dvija-bandhus are classified amongst the sudras and the women. Srila Vyasadeva divided the Vedas into various branches and subbranches for the sake of the less intelligent classes like the dvija-bandhus, sudras and women."

Srimad Bhagavatam Canto 1 Ch.3 text 22

Translation
"In the eighteenth incarnation, the Lord appeared as King Rama. In order to perform some pleasing work for the demigods, He exhibited superhuman powers by controlling the Indian Ocean and then killing the atheist King Ravana, who was on the other side of the sea."

Purport
"The Personality of Godhead Sri Rama assumed the form of a human being and appeared on the earth for the purpose of doing some pleasing work for the demigods or the administrative personalities to maintain the order of the universe. Sometimes great demons and atheists like Ravana and Hiranyakasipu and many others become very famous due to advancing material civilization by the help of material science and other activities with a spirit of challenging the established order of the Lord. For example, the attempt to fly to other planets by material means is a challenge to the established order. The conditions of each and every planet are different, and different classes of human beings are accomodated there for particular purposes mentioned in the codes of the Lord. But, puffed up by tiny success in material advancement, sometimes the godless materialists challenge the existence of God. Ravana was one of them, and he wanted to deport ordinary men to the planet of Indra (heaven) by material means without consideration of the necessary qualifications. He wanted a staircase to be built up directly reaching the heavenly planet so that people might not be required to undergo the routine of pious work necessary to enter that planet. He also wanted to perform other acts against the established rule of the Lord. He even challenged the authority of Sri Rama, the Personality of Godhead, and his kidnapped wife, Sita. Of course Lord Rama came to chastise this atheist, answering the prayer and desire of the demigods. He therefore took up the challenge of Ravana, and the complete activity is the subject matter of the Ramayana. Because Lord Ramacandra was the Personality of Godhead, He exhibited superhuman activities which no human being, including the materially advanced Ravana, could perform. Lord Ramacandra prepared a royal road on the Indian Ocean with stones that floated on the water. The modern scientists have done research in weightlessness, but it is not possible to bring in weightlessness anywhere and everywhere. He can make the gigantic planets fly and float in the air. He made the stones even within this earth to be weightless and prepared a stone bridge on the sea without any supporting pillar. That is the display of the power of God."

Do you mean to say that the sacrifices made in The Ramayana are for demigods and has nothing to do with we ignorant humans ?

No the Ramayana is the historical narration of how the Lord incarnated as King Rama to perform pleasing work for the demigods.

Introduction to Srimad Bhagavatam page 11

"In fact, in Kali-yuga all yajnas (sacrifices) are forbidden because they are useless attempts by foolish men. In Kali-yuga only the sankirtana yajna is recommended for all practical purposes."

Srimad Bhagavatam Canto 1, Ch. 4 text 25

Translation
"Out of compassion, the great sage thought it wise that this would enable men to achieve the ultimate goal of life. Thus he compiled the great historical narration called the Mahabharata for women, laborers and friends of the twice-born.

Purport
"The friends of the twice-born families are those who are born in the families of brahmanas, ksatriyas and vaisyas, or the spiritually cultured families, but who themselves are not equal to their forefathers. Such descendants are not recognized as such, for want of purificatory achievements. The purificatory activities begin even before the birth of a child, and the seed-giving reformatory process is called Garbadhana-samskara. One who has not undergone such Garbadhana-samskara, or spitiual family planning, is not accepted as being of an actual twice-born family. The Garbadhana-samskara is followed by other purificatory processes, out of which the sacred thread ceremony is one. This is performed at the time of spiritual inititiation. One who has been able to undergo such important samskaras can be called a bona fide twice-born.
If the father and mother do not undertake the process of spiritual family planning and simply beget children out of passion only, their children are called dvija-bandhus. These dvija-bandhus are certainly not as intelligent as the children of the regular twice-born families. The dvija-bandhus are classified with the sudras and the woman class who are by nature less intelligent. The sudras the woman class do not have to undergo any samskara save and except the ceremony of marriage.
The less intelligent classes of men, namely women, sudras and unqualified sons of the higher castes, are devoid of necessary qualifications to understand the purpose of the transcendental Vedas. For them the Mahabharata was prepared. The purpose of the Mahabharata is to administer the purpose of the Vedas, and therefore within this Mahabharata the summary Veda of Bhagavad-gita is placed. The less intelligent are more interested in stories than in philosophy, and therefore the philosophy of the Vedas in the form of the Bhagavad-gita is spoken by the Lord Sri Krsna. Vyasadeva and Lord Krsna are both on the transcendental plane, and therefore they collaborated in doing good for the fallen souls of this age. The Bhagavad-gita is the essence of all Vedic knowledge. It is the first book of spiritual values, as the Upanisads are. The Vedanta philosophy is the subject matter for study by the spiritual graduates. Only the postgraduate students can enter into the spiritual or devotional service of the Lord. It is a great science, and the great professor is the Lord Himself in the form of Lord Sri Caitanya Mahaprabhu. And person who are empowered by Him can initiate other in the transcendental loving service of the Lord."