Then we see the game and it's a completely white guy. "What? White guys can come from Africa too". /s
When I was working in games we had VERY long discussions about using a black main character, and ended up going with another White main character, simply because women and black men do not sell as well as white men. And before you quote a long list of examples that prove that wrong, first realize there's hundreds of games that fail with both. And many of the success are stuff like Metroid (They hide her face for the entire first game, rarely show her, and is by Nintendo who could make a game about Peaches PMS cycle and it still sells... and did) or Sony (Who has enough money and clout to advertise the fuck out of something like Horizon), or overly sexualized character (Tomb raider's first titties... sorry Titles)
It's still likely a wrong assumption but there's a lot of proof that the race of the main character DOES matter.
Pretty sure the biggest driver for sales in games is more often than not whether the game actually good. If your game doesn't sell odds are you made a shitty game. Blaming sales on the race/sex of the character sounds like a massive cop-out.
Falling under what I said before, one of the biggest series of all time, with massive marketing budget (After GTA 3, Rockstar really started to spend that for advertising.)
It's like the movie industry, ethnic minorities mean less revenue. At least the black people in the US are getting some spotlight that isn't the stereotypical ethnic/fetish treatment after a long time of struggle.