Refusing to date someone of your own race, is it self loathing, just a preference, and or bias?

I know a few people who won’t date there own race. Some say its because their personality clash with people of their own race, some say its just a physical preference and some say its more of a class thing.
So it got me wondering if perhaps it is more of a self loathing of their own race.
When I was dating, I didn’t draw the line at race. It was always a personality and chemistry issue. Did I have a preference. Yes, but even then, I would date a guy if I thought we mesh well and he was a nice guy.
So is it just a preference thing or are they being biased?