I'm not sure how these services operate, but I wonder if a difference to traditional hotels is that they get applications, rather than reservations on a first come, first served basis?

If AirBnB landlords receive applications, maybe they just wait for an attractive one (ie a single male landlord could prefer to rent to attractive women).

I'm not trying to defend racism, just wondering how to alleviate the problem. I suppose traditional hotels don't get to look at a profile of the people who book with them. At most they could infer something from their name.