I thought he was in a new episode of Family Guy

Subversion is still an excellent choice.

Maybe a question with an obvious answer, but why are there not yet more data centers in Africa?

I believe it's a combination of a lack of customers and lack of infrastructure. It's a big continent to cover with the necessary fibre capacity, and the market is much smaller for nearby services.

Also what you don't see in things like this, or even a list of datacenter locations, is the relative sizes of the datacenters. After US east/west coasts and Europe, datacenter capacity rapidly tails off. Parts of Asia have plenty but not on the same scale I believe (although I don't know about the Chinese market). The difference in size can be quite a few orders of magnitude between different regions.

Smaller market, less reliable power grids, more challenging heat management, less political stability in many african countries. Also, given their pricing, big cloud vendors AWS are a luxury many local businesses would probably not even consider.

This isn’t just an issue for cloud providers. It’s also not easy to find collocation space either.

My best guess is that it is a combination lower demand (vs rest of world), and infrastructure availability (connectivity + power).

I can imagine a bunch of secondary factors too, but this to me sounds like the key broad reasons.

Sheet of what?

Question from the uninformed here: Is this just a change to how the statistics are tallied, or does this trigger a ripple effect compelling service providers to do something differently?

The author goes on further about this about half-way through.

Is there somewhere we can see submarine and land cables both?

Land cables are usually considered classified/sensitive information, so no not generally.