I almost always mix it up, one game I'll play as a black guy, next a white guy, then a Asian girl etc etc. It really boils down to what game I'm playing and what I decide to play as in that moment.
GTAonline main character is Hispanic.
Skyrim main character is white.
Saints Row character is Asian.
Division character is black.
Andromeda character looks mixed race, white and Indian.
I definitely play as a white dude with dark brown hair more than anything though since that's what I look like so I tend to gravitate towards that more often than any other race or gender.
I see nothing wrong with people only wanting to play their own race and gender and those who like to mix it up, or just play a single opposite race and gender carried over throughout many games. I think it's a good thing to be honest, I love character creations for that reason alone, I, or you don't have to play as someone's pre-set vision.