The thing is that i'm guessing a lot of punters possibly almost all would see no reason not to Bareback the dolls whereas they wouldn't contemplate Bareback with a person.
Depending on how well they were cleaned or indeed if they were cleaned you could end up doing a bareback punt with anything between a wet wiped doll and full on sloppy seconds.
Also the dolls are probably doing back to back bookings so everything would still be warm