I think people just get used to it being one way because of being unable to change it in a game they play often and that's how they keep it when given the choice.

I prefer inverted for third person but not first person. In first person you are seeing through eyes, when you move them right, you should be looking over to the right. In third person you are seeing through a camera behind the character, when it swings in a half-circle to the right, you should be looking to the left.

I absolutely can not stand it when one axis is inverted and the other is not.