Cause they can? I'm a woman irl and my main and secondary alt are Male Roe and Male Au'ra (though he's a bara cat right now) and then I have my main alt and third alt Fem Roe and Fem Elf.

It's not that deep. Some have played as male or female avatars for so long maybe they wanna change? I'm sure lots of guys might've played as the girl trainer when Pokemon Crystal came out cause it was the first Pokemon game that let you have the choice.