In my case, it's mostly just that I tend to play against type.
Most people expect the front line tank to be a scary space-marine dude in a sci-fi setting. Which is exactly why I go with a petite, optimistic young lady wearing a ten foot tall war machine who continually quips while keeping anything from bothering the squishies. When I go wizards or healer types? Technical types? I tend to roll with men who know exactly what they're doing and have a fair amount of experience going with them.
Where rogues would be slinky women in leather armour by stereotype? I'd go with a middle-aged veteran who wears street clothes and capitalizes on his skill at ambush to resolve problems. Where barbarians would be bare chested conan dude sorts? I'd go with a short-tempered victim of the old "Oh no! My beloved peasant village!" shtick wearing practical mail and compensating for her lack of skill with ferocity and enthusiasm.
It's just how I roll--sometimes it works, sometimes it doesn't.