The reason they are talking about 4-plexes is that's the reality of redeveloping a single family residence one at a time. If you could do it city block by city block there would be huge savings, and WAY more developer interest. The problem is it's too hard and expensive to assemble that much land to make such projects actually happen. No one wants to move, no one wants change.
The headlines will read "Poor Betty was forced from her home by the evil mayor and money grubbing developer".
They set the table when they built it, and to undo all of that is going to be crazy expensive and difficult.
Some people dream of a car free utopia. Some people like their SFR. Those things may not be compatible.
Things like the Miami tower collapse will make things worse. A lot of people don't want their life dictated by their neighbors. HOAs are well known to be horrendous. And the Miami disaster just goes to show that not only can your HOA affect your sanity, but also your life safety.