Apartments can also have stuff you could never afford that a kid would like, such as a massive pool (try pricing out a new build pool these days).
And families do it in NYC, and Hong Kong, and Germany, and Spain (AFAICT, 65%), and…
Think about having to share a bedroom with your child, and when they're old enough to need their own one, putting up a partition wall and having each be less than half the size of a normal bedroom, very cramped. And you don't get a living room. (If you did have a living room, now it's your bedroom while the child gets the actual bedroom)
Okay, let's stop spending money on roads then.
How are you at riding your bike through mud? Pretty good? Got nice chunky tyres?
That's not actually true, and the paper that describes the "fourth power" thing even says that right up front.
If you massively oversimplify the model so that you've got all vehicles fitted with infinitely hard bicycle tyres on a perfectly smooth surface, it kind of works out, but not quite.
How do you plan on getting food?
How does food get to the shop at the end of your street?
Bicyclists were the ones to first push for paved roads:
* https://www.history.com/articles/good-roads-movement-bicycli...
* https://en.wikipedia.org/wiki/League_of_American_Bicyclists#...
Or a small town that is surrounded by farms.
Just avoid suburban housing as far as the eye can see with a limited number of roads everyone gets funneled on to.