> Obviously, every single existing property owner wants it to stop right now. Because more housing means more supply, means less money for them.

Upzoning actually increases land values, because it gives you the option to develop your land into a higher-productivity use (and hence higher potential rents).

NIMBYs in my observation tend to be anti-change; they bought with the neighbourhood a particular way and want it to stay that way. Upzoning brings in a change in the vibe and demographic that they don't want.

Exactly. Most people don't buy a home with the hope that the surroundings will change drastically. And of course is there is a change for the better, the same people who complain about about NIMBYs will complain about gentrification.