I grew up in a Texas town of 100,000, and it didn't have a single bus route until I was 14. The closest shop was a small bakery six blocks away, which was a godsend since that was the only shop within five miles. When half the usable space is parking, it's low-density. When you have houses plopped in the middle of a hundred-foot-to-a-side rectangle, it's low-density.

I acknowledge that it is, indeed, a gradient. But lots of points on that gradient are huge negatives to the people living there.

I think what you're describing is a lack of public transit, not the impossibility of it. And I'm not 100% sure why 1/2 the space would be parking, this seems like a fairly large exaggeration. More likely lots of the space, was lawn? Space between houses?

I've lived in lots of cities where minimum lot size was an acre, which is 200x200ft. Public transit all around, grocery stores all in walking distance (few blocks at most), with loads of corner stores, etc.

I think that as I mentioned in another comment, zoning laws are important. Too much? Too little? It becomes broken.

But for example, large-scale developers typically can't build here, without dedicating some space to park, to retail, without making an actual community out of the place.

And people in most rural areas I've lived, typically aren't bad off for it.

This may be a cultural thing, or a historical thing such as, how cities were build, and therefore, how they are now.

edit:

An added thought here.... when I visited the US, I noticed that a lot of grocery stores were often larger. I've seen some where it's literally a few minutes to walk end to end, when inside.

Maybe this is the difference?

Most of the grocery stores here are smaller. Maybe we just have smaller grocery stores, but more of them?

Yes, that's precisely the issue with American towns, and detailed in the article. Half parking is not an exaggeration - Walmart in my hometown is a three-acre store with 600 parking places. This is not unusual - the Home Depot is similar. burger king is similar - more parking than space inside. The houses bring down the average. Lawns are in addition to this. It's hard to overstate exactly how sprawled the median American town newer than 1950 is, where you do have entire subdivisions without a single store. Sometimes multiple subdivisions in a row. No thought is given to community.

The article is calling for the exact type of mixed zoning you're familiar with - occassional shops mixed in with the houses. It's not like that, but it should be.