I think it's similar to what happened when left handedness was destigmatized. Suddenly, there was a sharp increase in the number of people saying they were lefties. It wasn't that more people were becoming lefties. It was that more people felt free to be who they really were.

A trans person 100 years ago couldn't really come out as trans. If they did, they'd likely face a violent response. So they lived their life in suffering - maybe not even knowing why they felt so different from everyone else and thinking that there was something wrong with them.

As being trans is destigmatized (and hopefully the anti-trans stuff recently is short lived), more and more people will "come out" as trans. It's not that the actual number of trans people is increasing, but that trans people don't feel like they have to hide who they are. Eventually, like lefties, the rate will level out and stabilize.

A hundred years from now, people will be referencing trans people instead of lefties when talking about the next marginalized group that's being destigmatized.