I'm going with there's a bubble. All these clack collectors/hoarders are seeing the rush of new people producing unique caps and know they might be producing them in limited runs as well. When you have Brobots V2, Domo caps, Binge caps, and I'm sure a few others coming out and many, especially Domo's, are looking to be high quality, it really shakes up the market. Now there is more competition in that niche homemade novelty cap market and it's not just Clacks and the meh Brobots.
Not only that, but there's been an influx of more mechanical keyboard users and more people willing to pay ridiculous prices, so they know now's the time to sell high. There will come a time when people just get sick of it and decide that it's not worth it anymore, not at hugely inflated prices that are lining the pockets of some greedy people (not all sellers are greedy, but some are).
Similar thing with the Korean keyboards. People see all these awesome metal cases coming out domestically and cool domestic or more local keyboard projects and don't really see a reason to go with the more expensive Korean custom keyboards, especially when the market is starting to be flooded with all these other awesome options that also happen to be cheaper than a Kmac and the like without being any lower quality.