In major high cost of living American cities, the majority of cost is in land and regulatory uncertainty especially in California - years of lawsuits and public comment hearings etc for any changes to the built environment, zoning restrictions, large parking requirements causing more land to be needed, inability to produce dense housing (and therefore more units to rent out) on any parcel of land, and so on.
It’s hard to change these policies in part because the basis of American wealth for most people IS the value of their real estate, so anything that would reduce the cost of a house will also reduce the wealth of a large swath of society. And rent control warps thing, by making existing renters also benefit from the status quo by locking in their rents, leaving only new renters as those who demand cheaper housing - the very people with the least electoral influence given that they’re usually younger and not established in the communities they’re moving into.
We need ways to align incentives so that these people can clearly understand their personal benefit from the good that densification would bring, alongside a reorientation to base their wealth on something that isn’t shelter.
USA is not the only place with inflation, but it still ends up with housing far more expensive than other countries. That’s because of policy primarily, material costs secondarily.