BBC and anal

My husband has recently revealed his fantasy to me regarding this lifestyle. We are in our 50's....I am fine with it and we have found a BBC and will be getting together later this month. He is everything we could want mentally and physically. My question is this....why is it that the majority of BBC's that we've talked to seem to insist that I be anally trained? I have no experience in this and hubby has started gently working toward that goal. Our BBC does request that I be trained....what is it about blacks and anal please?
Thanks !