An interesting thread. In my view, it is a matter of how the sexiness of the subject if portrayed and/or if they are objectified. Being sexy and sexism are not directly related.
Here is the idea behind it. Male gamers, like males in general, look up to and idealise men of a certain type, whether these are football stars, movie characters/stars or game characters. They are of a certain role model like type. Usually rugged/grizzled, fit and 'manly'. This includes usually being good looking. Nathan Drake being the prime example.
There is no reason why female gamers automatically want to play as your average Josephine Bloggs is there? They would want to play as a strong willed, independent female character that is also 'sexy', not only in the fact she portrays herself in a certain manner but by the fact they look good too. Lara Croft or more recently Nilin from Remember Me being good examples.
The problem would be when that sexiness is exploited for objectification. Megan Fox in Transformers movies does nothing but look pretty really, she's even lead about La Buffs character by the hand on numerous occasions even though she was meant to be this bad-ass car loving girl, independent from her 'man' earlier in the film. The Metal Gear 5 character from earlier is a great example of objectification, half naked for no reason. Dead Or Alive Volley Ball but at least that doesn't hide from it).
Sadly, to do that with males is harder to do because of the games industry. Male dominated in development and market.
Hmm, pie.
