Internet usage is soaring in Nigeria. It is a major African country. But I don't think there is an aftermarket for .ng domains yet.
Nigeria also has a reputation for being very corrupt.The registry itself has been accused of wrongdoings, confiscating domains etc. And there a few other countries where the rule of law is shaky, and the registries apparently acting shady. Put simply, many exotic registries are poorly run (like any other state institution...).
Speaking of Africa, many of its TLDs are still embryonic, the regs are measured in hundreds or thousands. Eritrea has fewer than 100 active domains in .er...
I think that when you venture into ccTLDs, especially the more exotic ones, you need to know the local market well enough.
BTW: each ccTLD is different. The rules on what is allowed/forbidden may vary a lot from one extension to another. Some TLDs do not allow speculative regs for example.