They do [0], for each batch. Not quite at the level of granularity where you can reduce scope from everything they fund to just look at US founders, but the general trend appears towards increased diversity, and it looks like that's a YC goal as well.
Those statistics are very spotty and incomplete, though. They start with W15 but have nothing about 2016, for example. The format isn't consistent from one post to the other. They often (although not always) only give the percentage of "companies with one female founder" instead of the total percentage of female founders. They list the countries of origin but with no percentage at all except for the US.
Most importantly, they don't list the level of education of founders, which I think would show they are not primarily helping the disenfranchised.
YC is a business. It makes sense that they would choose healthy founders with high education levels, high IQ, drive, grit, what have you. They are a business, not a charity. And that's fine.
But the claim that they are making the world a better place is a bit rich. If (for example) you're funding crypto -- including NFTs! -- you're not doing that for the betterment of humanity.
[0] https://blog.ycombinator.com/category/batch-stats/