This is pure idle speculation on my part, but I sometimes wonder with the extremely high prices of some morphs, whether the price more reflects the breeder's willingness to sell an animal, or drum up interest and future sales. They are mostly planning on holding the fancy snake back, but would be willing to sell if someone really wanted it for $$$$. In the meantime, it's listed on the website for $5000, attracting interest and creating a perception that it's the hot new desirable thing and worth a high price. And then later when there are a few more of them out there, people will happily fork over $800 for its babies and feel like they're getting a bargain.
I have a hard time imagining that a gene would die out and disappear because it was too expensive to get popular, unless it was also prohibitively expensive to work with. And the only ways I can think of for that to be the case would be that most of the babies died or all required extensive/expensive intervention of some sort, etc, in which case the gene probably deserves to die out anyway.