1. Money Laundering: If you made money from a pump and dump or something otherwise nefarious that you want to convert back to USD and explain away, a good way is to mint digital art and sell it to yourself. Then when you report it to the IRS you made $100,000 from selling digital artwork to an anonymous buyer instead of from insider trading a low market cap coin. This is not so different from how art works in meatspace (see Mark Rothko).

2. Charity: It's hard to really grok this if you don't live in the crypto world but people make insane amounts of money from Ethereum. I know multiple people who are under 30 and have each made upwards of $500,000,000 from buying ETH in the presale / insider trading in bull markets. Generally someone who bought into the ETH presale is a mega crypto bull and keeps a large percentage of their net worth in crypto. It's trivial for them to support artists by buying their artwork for a minuscule fraction of the money they've made. What sounds like "buying a .jpg for thousands of dollars" to someone not in this world, is more like the crypto equivalent of tipping a live streamer a bit on twitch.

I don't understand it either, but they actually pay for a certificate of ownership of a .jpg or .gif, whatever this means.