I feel like it happens because they are unfortunately also easier to discriminate. You can’t hide being black. Middle eastern people can easily pretend to be something else. I’m Sephardi jewish. But could pass for Greek, Latino, Persian, Spanish, Arab, Portuguese. Dick size is irrelevant cause what happens if you’re white with a big one? Same with pimps many pimps are non black. But as mentionned it’s still the girls choice. I’d rather a girl say no arabs (I could be considered as one and I saw same ads in the past that mentionning that restriction) or no blacks than accept and to give a crappy service. Another thing some girls hate uncut dicks but won’t mention it imagine how funny it would be. I’m sure some hate cut as well. There is also the argument about family or friends finding out but again client could for example say I’m Greek not Arab. Doesn’t solve the problem all the time.
My 2 cents could be not 100% accurate