90% of my female friends play male characters because they got bad experience in MMOs, other girls find male characters attractive and want to look at them, some others identify with that gender (mentally, physically, or both), and other just prefer the way how male characters look and their outfits.

At first, I didn't know they were girls. I don't go around asking for their gender. People tend to just say it later on or you hear them on discord. It's not like we ask people when we meet them face to face, "hey you were actually born a female/male or did you transition to be female/male?