There are several factors. Mining in one reason for the large demand. Another that has been suggested is the popularity of PUBG. People are upgrading their systems to be able to play that game better. Another issue is have you seen ram prices? RAM chips are also on GPUs and they are now packing not just 2 or 4GBs onto the card, but 8, 11, or 12GBs. With the ram shortage going on that is also adding to the cost of the cards. Finally, I've also seen it suggested that yields aren't as good this time around. If the yield rate is lower, ram costs more than it should or usually does, and people are buying cards for the new hot game/mining, that just leads to much higher prices.