I'm from the mountain West, live in a pretty small town that's been growing off the charts, following Jackson and Aspen as the rich and famous move in. Also have experience in tenant work and politics.
As others have said, it's pretty much classism/racism amongst yuppies and retired boomers. That said, the answer isn't go to fully YIMBY "build baby build!". For many reasons, zoning changes for things like affordable housing often increase property values, making things more expensive. Pricing is much more responsive to demand than supply (never mind that econ 101 rules don't apply like that), plus the whole market is designed to prop up property values infinitely. The American Dream enables this by convincing the middle class who can afford houses (or used to) that property values are going to fund their retirement (spoiler: it probably won't).
Until 1) cities can figure out how to stop chasing gentrification to get a wealthier tax base, and 2) regular people can be convinced that high property values are bad in general, we're fucked. We don't have the kind of cheap available land in the West + govt. subsidy that fueled the cheap single-family boom in the 1950's anymore.
Better than the original tbh.