First of all: don't they? (honest question, I truly don't know if Africa has more PWAs compared to US/EU/etc)

Second: There are many reasons why businesses would opt for a native app. Notifications, for one (not available on the web on iOS until just a couple of years ago). Also, native apps allow for more tracking (whereas browsers are paranoid by default).

Third: A few years back, companies like FB, Google and Twitter all launched "Lite" versions of their apps, specifically targeted at Africa and other developing markets. They were all web apps (or wrappers around web apps). I will admit that this was years ago, and I have not checked if these Lite versions are still around and/or widely used.