The use cases are more than art. Art is a part of the equation, sure, and we see these... incredibly inflated prices being paid for art as insane. Digital art. That can be replicated. In which ownership of the NFT may/may not convey ownership of the artwork. Of course this sounds absolutely nuts, and people can be forgiven for believing it is absolutely nuts and that's all there is to it.
But consider a very successful real world use case: trading cards. As NFTs, these digital cards are limited by contract on their respective blockchain such that infinite copies cannot be printed - they are limited edition. Scraps of cardboard for this rookie or that player only have ever had value to people who collect them - now the same sort of thing exists in the digital realm, without the risk of losing the physical collection in a house fire. It's less the artwork that is valuable, but the NFT itself.
Another valid use case is Patreon-like support of artists (especially in the music industry). As it is now, tens of thousands of people contribute money monthly to their favorite artists via platforms like Patreon often in exchange for perks like early releases to tracks or works in progress. NFTs can represent the same sort of thing, except that at some point in the future these early released tracks - or really - the possession of a fact of support for a band during their career as an NFT - has value amongst other fans. In some cases possessing these things can become backstage passes to a band at a concert.
Much of the NFT space right now is a cash grab. That doesn't mean valid use cases won't emerge.