Obviously this won’t work for all sports, but things like football, track, soccer, it would allow for de-gendered team, even allowing athletes with the skills but not the genetically-endowed physical attributes to have a place to play.
Note: I know very little about sports and being on a sports team, so please point out anything that doesn’t make sense.
because lots of (most?) trans people don’t want to be “trans”, they want to fit in with the gender they know they are, and being labeled as not a real man or woman in the normal sports leagues, but a trans man or woman in the trans league, is insulting.