Some men may roleplay as female avatars in MMOs to meet the real life woman of their dreams, but other males have a very different reason to do so:
In real life, I'm in my thirties, overweight, balding, married with children. I'd blend in flawlessly at Penny Arcade Expo or any renaissance faire of your choice. In Second Life, I am a flirty cyberpunk chick who hangs out at clubs and has hundreds of folders of clothes. Yes, I know I am a stereotype. I am THE stereotype...
I am gender dysphoric. That is, I'm not comfortable with the gender I was born with. I look in the mirror and am always surprised that the guy staring back at me is actually me. I've been in and out of therapy over the years. But I live in a liminal state -- half in my body, half detached from it, half male, half female. Second Life is a haven for me. I can look at the screen and actually see a part of me that I always knew existed, but could never point at. I can sit and talk with other women and be treated as a sister, not a potential predator. I can enjoy being beautiful (a feeling I've never had in RL), because even if that beauty isn't real and I bought all the parts off of [the SL Marketplace], the combination is something that I created and expresses me. It's a "me" that cannot exist in any other sort of environment. I'm not trying to deceive anyone. I am not trying to live a lie. I am trying to live the truth, in its entirety.
From "Second Life's Strength Is Its Power To Transform Identity -- And The 'Weirdos' Who Embrace It", a NWN guest post from 2010.