Now for a NFT, the problem is that it is not fungible, so you would have to open a LN channel for each NFT, because each NFT has a distinct value and market, so you (probably) can't bundle various NFTs into one channel. In most cases each account holder won't interact that much with a single NFT, maybe a handful of times as a maximum, so the benefits for Lightning are limited.
Why not? We are talking about smart contracts here and all it takes is two parties who accept the token to agree on an exchange rate, then they can "swap" their tokens with each other with that rate. I think the same principles of Atomic Swaps can be applied here too.