It's not poor planning, it's what Americans want. Americans, by and large, do not want to live in dense neighborhoods or tiny homes like in many parts of Europe. You get that in places like NYC and quality of life in those places is atrocious.
There are probably even more people who would move if they could, but our cities are expensive (because housing is expensive when you don't build it) and so they stick with the "default". Staying put, getting a car, and finding a way to make it work.
You can't conflate "this is what Americans want" and "this is largely the only choice most Americans get".
At least around where I live (DC suburbs), every dense neighborhood becomes tremendously popular. The limit is that planners are very reluctant to allow them to be built. No problem getting permission to build an 8,000sqft house on a 1/4th acre lot though.
Americans are just rich enough and lucky with geography to be able to have them.