I can think of 2 reasons right off hand.
1> Moon clips are a PITA. Yes, they make for fast reloads which makes them a popular choice for certain shooting sports. But, for just going to the range and shooting, they are a PITA when it comes to clipping loaded rounds and unclipping empties. FWIW, that's why they came up with the .45 Auto Rim round -- to get around the PITA factor in .45 ACP revolvers using moonclips.
2> One of the advantages that revolvers have over autoloaders is that they are much less picky about bullet design affecting the feeding reliability of the weapon. If the brass is sized and the OAL isn't too long, the round will feed. That means that given otherwise equal potential autoloader and revolver rounds, the autoloader bullet must take into account feeding reliability into its design where the revolver bullet does not. That implies compromise in the design of autoloader bullets that revolver bullets do not have. We live with this when we use autoloaders and accept that implied compromise, but we do not have to live with the compromise when we use revolvers. That is, unless we are trying to use autoloader bullets in a revolver. I'm not saying that it won't work, because it does. But it entails having an inherent compromise that otherwise wouldn't be there. Of course, you can avoid that to a certain extent by handloading/reloading, but even then you'll find yourself in the position of not being able to find revolver optimized components readily available for autoloader rounds.
