I think the problem here may lie with trying to equate the popularity of an emperor with how common his coins in this series are. I don't have an answer, but I can suggest that how common or rare respective emperors' coins are are result of simple production logistics rather than how many coins of a particular emperor they actually wanted to produce because his popularity at the time. There's the theory that the whole series was produced at a single workshop at the mint. We don't know if all the coins were struck simultaneously, or in a certain sequence. Perhaps after they had made a whole batch of A-Pi coins, they cooled off for awhile with the MA coins?
Yeah, that's what Occam's razor says. <sigh> But it would just be so interesting and COOL if Commodus were more popular than his dad in 250!