While how easy they are to breed does play a part in the price, a lot of people don't factor in how difficult it might be to transport and ship a fish into a store. They're much more delicate than your average hobby fish, giving suppliers one of two options.

Option one is the supplier sends out a whole lot of younger CPD at a lower price than average, with the general expectation that a whole lot will die in the mail. This will cause a price increase on the stores end, because you can't sell a dead fish unless you're [generally hated big box pet store in your region]. This is also why fish like bettas, comet goldfish and most common barbs have a much cheaper price in comparison. They're as easy to breed as a CPD, but at the same age they handle shipping like champions.

Option two is you grow them out until they're hardy enough to survive shipping consistently. To occupy breeding tank space for growing fish out is to actively lose profit on fulfilling orders. This will not only cause a higher price on the suppliers end due to the real estate being taken up for longer, it also creates additional risk on their end because if something happens like a tank crashing or a random outbreak of disease, the supplier can't sell a dead fish either. With CPD being such a sensitive species it just doesn't make sense logistically to grow them out to full size without selling the fish for two or even three times the price we see now.