The reason P2P trading is so popular in Africa is that the central banks in most of the countries have prohibited their banks from servicing bitcoin/crypto exchanges, or even customers that are found to be engaging in trading of bitcoin/crypt.

So P2P is about the only on-ramp and off-ramp into and from bitcoin/crypto.

Mobile money is very widely used in many countries, and it works well as a payment method because those payments are not easily reversed, and are not part of the banking network so the central banks are generally permissive in letting mobile money continue to be used in P2P trading activity (i.e., not jailing or pursuing). But there are exceptions: Nigeria has undercover agents buying bitcoin from P2P traders and then reporting them to the bank, which closes the trader's bank account, though criminal charges are generally not the result).