I thought this article does a good job explaining why some people care a lot about this topic https://www.theargumentmag.com/p/how-youth-sports-supercharg...
The problem for this argument is that there is no actual data that trans kids and specifically trans girls are any better at sport than other girls.
Literally no trans athletes winning anything. I think hacker news skews scientific so we can do the math, if say 1% of the athletes are trans we would expect them to win 1% of the medals in a fair contest. As it is, they don't even come anywhere close. There has not been a single olympic medal won by a trans athlete, so clearly they do not have some kind of magical advantage, in fact (and common sense would make this pretty obvious) they seem to have quite a statistical disadvantage.
On this topic, I feel like "why do some people care a lot about this" is probably the question least in search of an answer.
That article does seem very one-sided:
> of youth sports have created clear incentives for them to prioritize competitive fairness over principles like inclusion, well-being, and fun.
In an event that is primarily focused on competitive fairness, what does inclusion have to do with it?
If playing sport is about fun, well-being, etc, then don't play in competitive events. You can't very well want to play in competitive events while complaining about competitive fairness.