Permits and licensing is a huge factor, most of the southeast didn't even have licensing boards until the late 90s. If you wanted to build a house you could just do it. Now it's functionally impossible unless you are capitalized enough to spend a considerable amount of time and money on the permitting and approvals process.

One of the reasons there's so much gentrification is that it's much easier for builders to take a falling down house and replace 99.99% of it than to get approvals for completely new construction.