Yes the number of girls who won't see black men is an eye-opener, I wonder why they won't. 
I've heard loads of different reasons, from size, to more likely to do something underhanded like rape or mugging the WG, hygiene, low balling, to trying to spend more time then the agreed upon rate. I think a lot of WGs use size as a reason because Atleast it isn't as condescending as the latter reasons. I've also seen quite a few black WGs put this up too.
Personally Aslong as your a black man that has good feedback I shouldn't see what's the problem is? Maybe a Service Provider on here could help us out.