If you take a typical median-income family, plot out a reasonable household budget and daily schedule, and then try to match it with every place in the US, most of the results will show that the family must own at least one car and spend an hour a day driving it. It's the only way to afford being there at all. The desirable areas are priced out of their reach, because there just aren't enough of them.
I'd love for all my daily transit to be on elevators and electric trains. But I also want my public school district to have enough money to pay its teachers without taxing me, specifically, into oblivion. For reasons I cannot comprehend, my employer wants to locate its workplace in the middle of a bunch of office buildings, where they enjoy lower facilities costs and a lower tax rate, while still benefiting from an educated workforce. So I pretty much have to drive a while between home and work.
If I lived close to work, I couldn't afford the place. If I worked close to home, the jobs nearby wouldn't pay enough to cover housing.
The median household income is roughly $60k. 86% of workers commute using a privately-owned automobile (ACS data), with about 3/4 commuting by driving solo. The mean commute time is about 26 minutes.
This situation might be exacerbated by the fact that the median tenure at a job is hovering just above 4 years, and home mortgages are 30 years. So if you buy a house and want to pay off the loan on schedule, you now have to make sure it is close to 7.5 different jobs in your industry. ...Per person working in your household. Married? Site your home near 15 jobs, some of which might not even exist yet. This doesn't even account for what happens when your company decides to build on a new campus for all of its workers.
By the home affordability rule of thumb that you can afford 2x to 2.5x your annual income on your mortgage loan, the median household can afford a house at $120k to $150k. Find a pile of those within biking distance of 15 different jobs in one or two careers that pay $30k to $60k per year.
You won't, outside a handful of large cities, and the majority of the US doesn't live there, as shown by the commuting data.
What percentage of the land mass of the US does that constitute? I bet less than 10% and that's being really generous.
3% as of two years ago, according to the Census Bureau.[0]
But that's enough to accommodate the people that want to live there, or at least close enough to take public transport into the city. I personally dislike city living, so I'm happy I'm not forced into it.
[0] https://www.census.gov/newsroom/press-releases/2016/cb16-210...