All of those things are substantial factors. Building codes are another big one - most of them have little to do with safety or health, but rather "buildings mu

All of those things are substantial factors. Building codes are another big one - most of them have little to do with safety or health, but rather "buildings must be of such-and-such minimum niceness, and if you can't afford that, too bad, go somewhere else." And everybody standardizes on the same building codes, and pretty soon there is no "somewhere else" to go to.