I mean, an NFT would tend to exist on a particular blockchain. If that blockchain forks (e.g., [as Bitcoin's done a number of times](https://www.investopedia.com/tech/history-bitcoin-hard-forks... )), then it's not unique, but rather exists multiple times -- potentially with different copies being owned by different folks. Plus folks could create duplicate NFT's of the same (by simply minting new ones), presumably on the same blockchain or/and others. And then, if an NFT is reliant on external-resources (like links to a host-server), as I've heard that most are, then presumably those could break and even if someone continues to "own" an NFT on some particular blockchain, the NFT itself would seem decontextualized and essentially meaningless.
Then, durability isn't ensured even on a continuous blockchain, as blockchains can elect to remove stuff (e.g., through forks or filter-protocols). Presumably blockchains would ultimately want to truncate historical stuff; it'd seem strange to assume that an NFT would necessarily be carried through such a process.
Then there's the non-optimality of primitive blockchains. This is, when there're innovations, we'd presumably expect folks to create new blockchains that may displace older ones, retiring prior-NFT's in the process.
Then if we're talking long-term, historic value, then we'd probably consider stuff like advances in cryptography mooting the original signatures, and just generally how ancient blockchains would seem to be of little interest to those in the future. Plus, I'd imagine that advanced AI artists would render the concept of trivial art being in any way non-arbitrary obsolete.
Long rant short, it's just weird to hear non-technical folks seemingly believing that blockchains confer "uniqueness" outside of more limited, subjective contexts.