[dagaci]

Until extremely recently Africa has (with the exception of the Nile delta) been very under-populated.

Even today it's regions do not rank amongst the most populated regions https://en.wikipedia.org/wiki/Population_density (with the exception of the Nile delta)

Historically Africa had very little population growth compared to the tiny population that survived the "out-of-africa" exit.

I would speculate: part of the reasoning for this would be the lack of domesticable livestock, and why that would occur in the place where humans had evolved from simple inefficient sapiens.

[hx87]

Scarcity of reliably arable land combined with extreme disease burdens probably have something to do with that.

[Frogolocalypse]

It's actually much more simple. It's just urbanization vs rural. As urbanization increases, population density can increase. Until very recently Africa was mostly rural.

[WildUtah]

With the Sahara and Kalahari, Africa will be desperately overpopulated long before it matches Europe or China for total density. There's simply a vast and growing uninhabitable fraction of land in Africa.

Increasing population pressure is actually already causing desertification that make it worse.