Well. There are two ways of doing it.
1. Customizing a character so that it looks like you. In this case, it’s for identification, not dress up. As long as the gamer is trying to hone the character to look as close to their appearance as possible.
2. Customization for entertainment. This case falls closer to a “dress-up doll.”
Both ways are mainly for identification purposes. Like when you customize a golfer on Golden T. You’re doing that, so your drunk friends can differentiate between their characters, and yours.
That being said, I think customization is a very normal, and not gender specific, behavior. If I put a bumper sticker on my car, it doesn’t make my car a dress-up doll. Perhaps there are similar subconscious motives for “why,” but I don’t see a direct correlation.