I won't dispute that race and class may very well have had influence on zoning laws. However, it's a rather fundamental human desire to own your property which drew people capable of making the move out to the suburbs - especially since it was affordable on a scale unseen before (good middle class wages, large houses selling for next to nothing, cheap transportation).

Hell, my dad was only a telephone lineman for Ma' Bell, and he could afford 5 acres of land and a house in (our city's version of) the burbs.

Regardless of future changes to zoning laws, not everybody wants to live in big cities. There's a strong appeal to live in a house of your own, where your children can play in the grass with their house pet. Where they can go to school with a class size where they have a chance to actually know everybody in their class.

If you really want to increase the density of cities even more, people will either require a) no choice but to move to the big cities, or b) a fundamental shift in thinking about owning their homes and raising their families.

And please remember that you will be working against eons of human nature when attempting to create that fundamental shift.

Speaking as a former child of the suburbs (one of the livelier and more walkable ones, with several nearby colleges), car-centric suburbs are awful for children, especially for those aged ~10–18: there’s nothing to do, and it’s impossible to get places independently. Parents end up constantly on the hook as chauffeurs, and kids end up with very constrained freedom of movement and very regimented schedules. People are so spread out there’s huge overhead meeting up. Kids with niche interests can’t find anyone local to interact with.

Kids in a denser neighborhood with easy access to public transit have much better quality of life on average. Parents who move to the suburbs for the benefit of their children might just be projecting their own desires.

As for “aeons of human nature”: for most of prehistory and then most of history, most people were either living in isolated tribes in the forest, or as rural peasant farmers. Not sure how either of those is relevant to considering parking requirements, building height limits, etc.

There’s no inherent reason for class sizes to be different between urban and suburban schools. Often suburban schools have more resources because the USA spends more money on public services in cities with wealthier residents. That’s unjust public policy, but nothing directly related to population density.

Lol, I don't think blackophobia is the primary driver for suburbs. Look at Billings, MT. .7% black and it is almost all suburb.

Lots of people just like having a little privacy and a domain of their own.

Montana is 600 miles by 250 miles and has almost no people living in it. It’s entirely unsurprising that people who choose to move or stay there want to take up lots of space. As for racial makeup: Montana was largely settled by people given free land in return for moving there, and then in the late 19th century a mining boom; during that era local laws were quite discriminatory. It hasn’t recently had any booming industry that might attract a wide variety of immigrants.

Billings is the largest city and has only 160k people. Billings is spread out along a federally funded interstate highway, and has plenty of available land. It’s a place with harsh winters that would be rather unfriendly to pedestrians/cyclists anyway. 95% of households own a car, and on average there are about 2 cars per household. (For contrast, in NYC there are about 0.6 cars per household.) As far as I can tell buses are the only public transit in town.

Small FYI - that mining boom meant that laws against races, religions, or otherwise meant remarkably little. The Copper Barons ran the cities, and all they were interested in was your labor, either in the mines or in support of the miners. Of course, this was also a time when the color of your skin mattered less than your place of birth. Irish and Chinese were held in equal contempt.

Even today, some of those mining towns are bigger melting pots of various races, religions, and cultures than the port cities.