It was inevitable that some kind of backlash would happen; you can only force people to pay so much for the places they live before they get mad and revolt. And it was predictable that the revolt would begin in California, the country’s most NIMBY state. YIMBYism is the form that backlash took.
The YIMBY movement is not a typical American movement. Its goals are narrower than most economic movements — it’s not about changing the whole role of government, it’s just about getting more housing. At the same time, it’s an ideological big tent — most YIMBYs are lefties (because most people in overpriced metros are lefties), but a few are libertarian types or fed-up businesspeople, and a few are hardcore socialists. This combination of narrow goals and freedom from broader ideology allows the movement to launch a pragmatic, multi-pronged assault on housing scarcity. YIMBYs want deregulation when it comes to things like zoning and parking requirements, but they also strongly support public housing and a vigorous role for state development planning. In other words, YIMBYs just want housing, and lots of it, any and every way they can get it.