The hype has just ceased. There wasn't any real product behind NFTs, nothing useful at all, so eventually it was a matter of time until they completely died. It's not like main cryptocurrencies which face cycles of highs and lows. Take Bitcoin, for an example, sometimes we see the price crashing, but after a while, it starts pumping again, because investors see it as a valuable asset, which is useful on long run to be held.

On the other hand, the same can't be said regards NFTs. Developers promised to sell a worthy asset, which was unique and would work like Bitcoin along the time. But reality shows the opposite. NFTs worked like a ponzi, where early investors bought cheap, but late investors could never profit from this, since initial investors dumped their NFTs as soon as profit was possible to be made, remaining the late investors with priceless tokens on their wallets.