So an NFT is a digital signature that is worthless unless it "makes a market for" itself. It is a pointer to an infinitely and freely reproducible resource, meaning the owner of the signature doesn't actually have control over the underlying resource, they just have "proof" that they "own" it. And the owner needs to convince other people that their "owning" the signature has value, so that other people will pay larger sums of money for transferring "ownership", or other people will be recruited into the market to buy more stuff.

Let's substitute "digital signature"/"NFT" for "tulip", or "star", or "moon crater", or "beanie baby", or "MLM beauty product". How is the market for NFTs any different from these essentially ponzi-scheme markets?

"NFTs allow digital artists to profit from their work!"

I mean, sure, but again, they are selling digital signatures with no inherent value that they need to "make a market for". The money they are making isn't because of their art, it is because their sales skills allow them to convince greater fools that inherently worthless digital signatures are actually worth something.

Would we say "selling stars enables amateur astronomers to profit from their work"? Or would we rather say selling stars enables scammers to scam people who don't know any better? Or charitably that selling stars enables charitable people to donate money to whoever is selling the "star", both parties to the transaction recognizing that there is nothing of value being exchanged.

The latter would be forgivable but it also seems highly unlikely there would be a large market of altruistic donators wanting to provide patronage specifically via NFTs. We have a large and robust financial system that is perfectly capable of facilitating low/no-cost donations. It seems more likely that illegitimate or shady capital needs ways to achieve liquidity and legitimacy. And the whole "supporting artists"/"allowing artists to prosper" narrative is a fantastic (and sufficiently complex) cloak that would achieve that while avoiding scrutiny.

tl;dr When a market for an inherently valueless, infinitely reproducible resource pops up out of nowhere and begins to rapidly inflate, it seems likely there's some sketchy stuff going on under the hood.