Why do a lot of the people I meet that act like girls, Talk Like girls, and have a girl avatar in the games I like playing or in their profile picture turn out to be guys?

This has been happening a lot recently on Animal Crossing and on Twitter recently. They call me and others "Besties" use cutesy anime and other popular girl characters in gifs or other photos.

And when I find out they are just dudes, I became a bit concerned, They usually put in the bio that they are females and not males irl and have boyfriends, I suddenly feel bad about the guy who is with them.