Most sex workers dont want to see blacks for the following reasons:
1) They dont want to be robbed.
2) They dont want the fuck and then refusal to pay that black customers bring
3) In many Asian cultures, it is seen as low and disgusting to fuck black men
4) Black men, in general, have larger penises and they dont want the soreness and time off related to the aftermath of fucking black customers
5) If blacks are hanging around an Asian incall, the neighbours will get involved and drive the girl out because the Asian neighbours dont want the problems associated with black people hanging around their condo buildings, business establishments etc
6) Blacks have a pungent, off-putting smell. If a sex worker has a black client, that will create an odor issue for the rest of the day or longer, and it will affect other non-black customers who will complain that the hooker smells foul.
You have to understand that Asians look down on blacks and see them as sub-human. They really dont want anything to do with blacks.