My understanding of the issue is that while walkable communities are in demand they are a minority and generally speaking, also a minority that is less politically active than single-family homeowners.
Pretty much everywhere has a political majority of single-family homeowners, and if each locality decides on its own it doesn't want to have multifamily housing, then you wind up in a situation where almost nowhere actually allows it.
This is so weird to read. My cultural bias is showing: I'm from the Netherlands. As most of you know, walkability is the norm here. And while the country is flat, so is the area described in this article.
Pretty much everywhere has a political majority of single-family homeowners, and if each locality decides on its own it doesn't want to have multifamily housing, then you wind up in a situation where almost nowhere actually allows it.