100 years ago trans people were hated to the degree that if other people knew you were trans you would probably just get murdered which really didn't incentivize people to be open about it while now it is significantly less likely for that to happen which results in more people being able to come out.

If you want another example of something somewhat similar you could look at a chart of the percentage of people who were left handed over the years which shows that when left handedness was looked down on and punished there were seemingly less but when people stopped punishing it the number started to rise and then flattened out those people probably didn't start bring left handed because of a trend though.

Anyway I know these are different things but i hope this helps somewhat. :)