The reason is simple. Basic network capacity is underdeveloped. Radio waves account for the bulk of communication. And most importantly, there's little to no direct connection between neighboring countries. So even if Google built a datacenter in Africa, it would not solve latency issues and might even make it worse because virtually all requests go outside of the continent.
Political stability is also a potential issue. If you're putting K-hundred-million dollars into a top-rate data center, risks associated with political instability become hard to stomach. Kenya is a great place to work, and quite open to outside investment, but had major problems two elections back, a scare at the last election, and ongoing problems with al-shabab. One of the best places to work in SSA, and still doesn't feel all that stable.
mostly true, but there is at least some undersea cable infrastructure to and between the countries. See https://en.wikipedia.org/wiki/WACS_(cable_system) as an example. Bottlenecks tend to be within countries where fibre is often not built out further than the capitals, especially in the poorest ones like Guinea and Sierra Leone, where I was working on networks this year. On the other hand, Cote D'Ivoire has a very good infrasructure, and internet is much more accessible than elsewhere. I believe Senegal, the digital powerhouse of the West Africa region, at least, has the same. But much internet is still only point-to-point microwave if you're lucky (and that supports telephone and mobile data communication backbones too), or VSAT, if you're not.
The reason for mobile banking being explosive in growth is linked to network speed and availability. Mobile banking in countries I've visited are operated by the mobile networks. Therefore, they don't suffer from round-trip issues as bank apps. Plus ease of use. They have more in common with PayPal than normal banking services.
