I'm attracted to blonde girls with blue eyes or brunettes with blue eyes. If they made some porn (and I'm sure it exists I just haven't dug around) with only blue eyed people, I'd totally buy it. It's not a fetish, just a strong preference. I also prefer pale skin over tan, also not a fetish. Having categories of porn helps to separate what I'll likely be interested in.
For example, I have a friend who is attracted to pregnant females. Cool by me, but I don't really wanna see a lot of pregnant girls in the porn I buy/watch. In the same way, one may not want to see other types of people in their porn. To me, the classification of white/black/Asian/preg nant/MILF/whatever is no different than saying "straight" or "gay" porn. It's just a way to separate it out. If you had a porn with a little bit of everything, you'd have to buy a lot of porn to get three scenes you were really into, you know?
I think overall that if you made a hodgepodge video like that it simply wouldn't sell and at the end of the day porn is a business. Making a nice, well rounded porn might be good for morale and such, but if it collects dust on shelves and the company loses money on it, it doesn't matter much.
That said, I have seen some that overdo it. There's no need to dehumanize different types of people in porn. Not all porn does this, but there is certainly some that does. That I'm not a fan of.