alt Hacker NewsAn NFT doesn't have to be just a link; nothing in principle stops someone creating a NFT that stores the full bytes of some digital asset directly on the blockchain, just as nothing in principle stops someone from creating a NFT that doesn't do this (or equivalently, a NFT whose on-chain content is simply a text hyperlink to something). The Bitcoin Ordinals concept of Inscriptions (https://docs.ordinals.com/inscriptions.html), which is an attempt to build a NFT system for Bitcoin, does culturally encourage placing the bytes of a digital asset into the Bitcoin blockchain, and the tooling around it assumes this model; but again nothing prevents someone from creating an Inscription whose contents are simply a link to something else.
And of course there's no reason why a NFT has to be used to represent ownership of some kind of digital art - there are other uses for NFTs, such as modeling transferable network permissions or resources.
Ultimately NFTs are a just a specific application of blockchain technology, to represent some kind of resource on a blockchain which could in principle be digital art. If people care about ownership of NFTs representing digital art, that's a social fact about what kinds of art there is market demand for; and whether it matters that the bytes of the digital art are on a blockchain or linked from somewhere else (where they could get taken down or bitrot) is also a social fact.
I actually agree that treating NFTs that merely contain a link to some bytes elsewhere that worked at one point in time is a pretty dumb thing to care about, or have a market for (and the use cases for NFTs where the bytes are actually on-chain are, at best, fairly limited, although I wouldn't say completely nonexistent). And certainly the NFT market of 2021 or so, which had a lot of such NFTs, was driven by a weird social mania and people attempting to grift upon that social mania. This has never bothered me though, because I feel the same way about many markets for physical pieces of art; and ultimately it needs to be possible for people to create markets for things I personally think are dumb or at least don't care about.
I don't think they were saying they found out all NFTs must only be links, just they found out the NFTs being peddled usually were. As you say, bytes are bytes regardless what they represent - it's just a lot easier to grift something like a 32 byte hash or a link on a chain because storing all those bytes in the blockchain would have been a damned expensive way to run a grift.
There is a difference between markets for things I don't care about and markets for things I do care a lot about, just not in a positive way. I don't think it's necessary to allow an open market exchange for phone scammers, for example, and it has nothing to do with how uninterested I am in buying people's information. Not all NFT had to fall towards that kind of thing, it's just there was so little practical usage actually being done that 99% of it ended up being that way.