That's not the reason. The infectious period is actually quite long. And average time to death from onset of disease is around 8-9 days. Initial symptoms aren't all that severe and often just mimic cold/flu fever and chills and last around 5 days before more severe symptoms appear. People are infectious from the onset of symptoms. A person remains infectious even after they die for a period of time as well.

The reason they don't go pandemic is because they aren't airborne. They require close contact with bodily fluids of an infected individual. The current outbreak in Equatorial Guinea is epidemiologically linked to funeral traditions where the body is washed by relatives before burial pretty much assuring direct contact with bodily fluids.