So many reasons. Nigeria has refused to be one nation. Tribalism and Nepotism is enshrined in Nigeria because of most northern, western culture. For instance; one in the west/north always prays to be in the good books of the king in order to become great in life; however, the easterner prays to be blessed in his skills in order to become great.
East wants to progress economically and compete with peers in the world. West only desires to surpass East. Whereas, North only desires to dominate the South. How can we remain one?
The hatred towards the east is too much. Even children in the west and north profess this hatred for easterners. Thus, a united future would surely cause more bloodshed.