The factors that enable influenza to cause sporadic pandemics do not exist with Ebola. Ebola is not airborne, it is not contagious before symptoms appear, and it is only transmissible through direct contact with infected bodily fluids.
In contrast, influenza is contagious by the aerosol route before symptoms appear. Many people can be infected in a short time.
Africa has some unique customs that are responsible for the spread of Ebola. They wash bodies and give them enemas in preparation for burial; funerals involve physical contact with the deceased. The people who get sick are typically those who take care of the ill, and those who go to funerals of Ebola victims. In the US, we isolate patients with highly infectious diseases, and family members would not touch or kiss the deceased during the funeral of a person who dies of such a disease.