This is especially true in north America where cities all went through a huge conglomeration effort in the second half of the 20th century and absorbed their suburbs.
The best walkable suburbs I've visited, Montclair and Red Bank in NJ and Ardmore, PA seem pretty sad, small, and boring in comparison. Fine for a visit, but I wouldn't wan to spend three days in a row there.
There's nothing wrong with small and boring, the major issue is that generally the overwhelming majority of US housing stock and zoning laws are geared towards picket-fence suburbia, to the detriment of people who don't necessarily want that. Plenty of people certainly want that, but it's probably not anywhere near like 90% of people in the US.
I grew up in a dense city outside the US, and even as a not-particularly-social child, I still had plenty of friends I played with and hung out with, and also had tons of interaction with adults. Meanwhile I’ve seen my cousins grow up in suburbs over the past 10 years, and they interact with maybe 3 non-family members outside of school, because everything is like a 15 minute walk away through winding suburb streets. That kind of isolation is not healthy at all.