Being gay or trans or non binary or whatever is not contagious. There is no reason for differing %, except the trend is very clear: The older the generation the fewer % are out.

It's because people are more supported and more able to come out.

More people aren't gay. More people are able to live their truth publicly.

* and based on your comment I will leap that you aren't a part of this community. The ugly truth is it is still very hard to come out for way too many. And dangerous. Look at the attacks on trans kids and talking about gender in schools.