A better question would be, did anyone ever even buy them to begin with?
This means that 79% of all NFT collections – otherwise known as almost 4 out of every 5 – have remained unsold.
That is, most of the NFTs included in the OP statistic were listed for sale by their creators, and never recorded a sale. Another important detail is that even for the ones that did record sales, there's no real way of knowing if those sales were real. You can easily make another crypto wallet and buy an NFT from yourself. For more elaborate wash trading, you can find someone with an established wallet to collude with. There are obvious reasons to do this too; building up a history of increasing sale prices could potentially dupe someone into thinking an NFT is a good investment, or you could launder money by selling an NFT to a 'dirty' wallet you also control.
Probably some portion of the market was "real", but the volume is almost certainly much lower than anyone is reporting. Statistics like what the OP article is quoting are just about totally meaningless.