My theory is that, despite the economics for using Pi's completely flipping to making it a ridiculous decision for most applications, the decade+ of tutorials, Youtube videos, forum posts, github READMEs, etc all describe using Raspberry Pi's as the way to deploy XYZ open source project is enough of a "moat" that it just keeps the demand high enough to suck up supply.
Also I don't think that people realize how good 3-5 year old technology is relative to the price. There's definitely a great arb there right now, and I think it's just going to get better.
The Raspberry Pi brand is wildly strong, but it's eroded for me because of scalpers and lack of availability - hopefully they can right the ship before it's tainted for good.