Colonization making English and/or French an official language of about 50 African nations means there are about a dozen options that present basically no language barrier and much smoother cultural assimilation than East Asia in general.
I'm not saying no African at all would go to the region. But they'd be near the bottom of the list even with comparable policies.
Acceptance, Opportunity, Racism, Xenophobia.
East Asia is much more backwards than the West in this regard and the west isn't exactly heaven. In South Korea and Japan, all foreigners get the short end of the stick but black/brown people and Africans get the shorter end.
All the open policies in the world won't reverse public sentiment so easily.
Immigrant are human. And knowing you won't have to watch people scuttle away when you enter a bus means everything when you have options.
You can believe Japan would be full all you want but I assure you it won't be because of Africans.
90 out of 54 is quite a high percentage.