I think its a subconscious choice, in the same way that you see some guys drees in drag on holloween, i think its the secret need to be a different gender than what they currently are. Probably because having a real life sex change is more expensive than a 64 dollar game or clothing for the one day holloween. Not to mention they hide behind a few reasons, 1 of which are "I'd rather see a girls ass then a guys ass." For a game, and "well i think its funny, you know dressing like a chick for holloween." For that. Me personally I prefer to have my in game character reflect myself, titan/human/male.