This may sound like as easy question but no one else has asked.
Are you keeping the Desert with the females all the time? That may be stressing him out if you are. As long as you're keeping him with one female for a few days then giving him a break for a week or so before rotating to the next female. I don't see what else the problem could be unless he doesn't realize its "time" for him to breed since you didn't cycle them. (or at least drop temps a few degrees). Or maybe he's infertile?
I had a 1000 gram Bumblebee male that WOULD NOT breed for me in 2011. I did not cycle my snakes and he was supposedly a "proven breeder". I assume that's what the problem was, although I don't know for sure. Cycling them next year may be a good idea. It doesnt take but a few degrees, so RIs shouldn't be an issue.