I thought web3 was supposed to be some kind of decentralized compute, where rather than run on your own hardware or IaaS/PaaS you could make use of compute resources that vary wildly day-to-day in availability, performance, and cost, because they were somehow also mining rigs or something? But it's "decentralized" because there's not one entity running the thing.

Web3 is a rebrand of crypto scams. The 20018 crash exposed the crypto industry to how wide spread its scams were. So the industry rebranded to "web3". Nothing changed.

The scam message was that so many people got rich investing in web2.0 companies like Facebook. You can get rich too by investing in web3 (shitcoins & NFTs).