It is interesting that, a company like FiiO can bring out a HP that costs $300 and has a carry case, a cable with a changeable connector (first time for full sized HPs, I think), and a proper tuning which many TOTL HPs that cost 10x the price fail to do. And what is more interesting is that, those HPs with horrible tuning are sold like candies among the audiophiles with deep pockets (HifiMan is one of the best in the market when it comes to tuning open back HPs, but their TOTL closed backs are big fails). I see people buy those things, jump up and down for how good they are, start buying DACs, amps, cables and other stuff to compensate the incompetence of the manufacturer, and then at some point they jump onto the next hype train and sell those accumulated nonsense for peanuts. Just like those fancy DACs that claim to make you "feel" -300 dB, but can get away with a distortion caused by a cheap power supply in a $10K+ device, which those fancy audiophile ears fail to hear.
When there is a TOTL hype every week, it is just normal that things lose such amount of value. It is just a bubbled up market in which many are incompetent and riding on the price hike wave. The issue is not why HEKse is suddenly so "cheap", but it was that expensive in the first place. Again, I think HifiMan is one of the best brands in the HP market. I wouldn't lay fingers on many other brands that are so hyped. There are cable companies that sell cables for several thousands and claim to have made some research and came up with such a brilliant idea that can improve the transmission in some magical way - as if they have chemists, physicists, electrical engineers among them that publish papers and gather patents in those fields every time they release a "product". Even their claims are conflicting...
So, it is just normal that products in such a hype driven market lose value and you have such sudden changes in prices.