I don't think these people do it just to win at sports. They are just freaks and perverts who happen to be athletes. Athletic competition also has become a battleground for tranny issues because it's very visible and trends toward objectively determining who is better.

It's not like it being easier to win at sports is the only benefit to being treated like a woman. Hugely more scholarships, affirmative action hiring, affirmative action promotions, any man criticizing you is automatically considered sexist and wrong, preferential treatment if you're starting or running your own business, people including the police are more likely to come to your defense and believe your side of the story in basically any conflict, an endless supply of simps who would happily pay for you to live at home and do nothing, pro-woman groups and programs at every level of society, and of course all the left wing assholes who can't decide whether you're more stunning and brave because you're a woman, or because you're trans. Aside from having to live a lie and triggering every normal person's uncanny valley response, there are a lot of good reasons to pretend to be a woman. In the right situation I'd definitely check that box on application forms if I thought I could get away with it.