Earlier quoted context omitted.
Your thesis is flawed. It is illegal to build new dense walkable neighborhoods in almost all of north america. But existing neighbourhoods of that style tend to be both highly priced to live in and also popular tourist destinations, implying high desirability. The older east coat cities built walkable neighbourhoods before they became illegal.
I've never dealt with a city in my region that didn't have variance procedures for building and land development permits. In my own experience, these committees are nearly a rubber stamp unless an adjacent property owner expects to be inconvenienced. You're observing what's called realized preferences. Coffee-table planners seem content to frame everything as a political problem, as if developers are an extended civi…
https://strongtowns.org has a few good examples.