I wouldn't even say it was 'black culture' thing, this is just appealing to what we USED to have as back when food security wasn't as much a thing, actually having some weight was attractive as it showed you'd secured a reliable source of food, something for future children.

Once food security especially food preservation became a lot more reliable, that went away for more focus on being optimised like stronger, leaner and better endurance. You can see this difference throughout the centuries of cultures with better food security from the Greeks to renaissance to their depiction of female beauty compared to tribal depictions of female beauty.

So it is wired into us but 'thicc' as you describe is the other side of the coin as anorexic, that and obese are ways to enforce standards that would not make the population strong as how many times have we heard 'gyms are right wing'? As think about how they psy op black men with fat white women?