You have already answered your question. It's a hype and like all hypes, they have a duration. Just like when the ICO and subsequently, the DeFi hypes came and went. I think the NFT hype is ebbing. Sales dropped
Everything will obviously subside in time when the users have started to dwindle and the fans have started to switch to new things that are better and also profitable, so it is very normal for this to happen to anything new in the crypto space.