I think it's purely that most kids writing school reports are more likely to be asked to write about "African-American inventors" than "America inventors" or "Chinese inventors" or any particular country, and SEO-optimized blogspam has adapted to that. I don't think it's political.

Bing Search, which has an independent web index from Google/Bing, has the same issue. It's interesting how search results can be biased without any malevolence or even any intervention by search engines.