Imagine being a drug dealer, a corrupt politician or someone else who has to launder large amounts of money. If you have no source of funds you might have problems cashing out or be investigated. Solution: NFTs.
Create some stupid pixelated NFTs, and put them for sale. If someone wants to pay for 1 kg of cocaine, they buy the 10 ETH NFT. If someone wants a pistol, they buy the 5 ETH NFT. If you want to bribe the local politicians, just buy one of their NFT. This money transaction looks perfectly legal from the outside.
Someone can make the same NFTs link to cute cats on the clearnet website, but to cocaine, guns, and bribes on the onion version. This way you have a decentralised darknet market functioning in plain sight.