This isn't unique to cars - trains could give the same, but we already have a road network.
I think the same can be said (to a lesser degree maybe) about cars, which are very space inefficient. With enough sprawl and a certain density, e.g. in Toronto, it's just gonna be traffic for every one.
Cars don't enable many people to own 100 square miles - but I can get pretty close if I settle for 5 acres in an exurb. Many find that a single family house gives them close enough (they get a small garden - most likely grass they mow weekly - which is all they really want). But again it is a compromise. If we had science fiction technology (terraform Mars and Venus; teleporters) that 100 square miles might be reasonable.
Torotno exists, so of course car dependency is somewhat feasible in real life. The impossible part is travelling in the sprawl with relatively short time, as limited by the road's speed limit. The real limiting factor most of the time is traffic, because of the space inefficiency of cars.
I made this point because I seem to recall a city simulation game despawn cars (literally physically impossible) to make car dependent designs "work".
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> you can reach enough of a city to consider it all the advantages of a city
With enough people driving downtown you lose most of the advantages, and it makes the lives of those who didn't choose this lifestyle worse.
If everything around you is built with base assumption that you must have a car, then the optimization was done by someone else with a different definition of efficiency.