I don't think most of them want isolation, I strongly suspect that most people moving to suburbs are doing so for their career, as most well-paid jobs are in metropolitan areas. In a metropolitan area your options are mostly: 1) city 2) suburb w/ very little mixed-use zoning
Cities tend to be more expensive for less space. There are going to be many people who would want to live in a city with their family but simply can't afford the rent, so they live on the outskirts of the city (suburbs). Alternatively they may want the space, yard, etc. that a house provides, but this doesn't mean they want isolation. They may very well prefer suburbs with good mixed-use zoning and public transit, those are just very rare in the US.
> It seems that if you took suburbs away from these people
I'm not proposing taking suburbs away from people, nor are the vast majority of urbanists. We're proposing more ability to build denser suburbs (i.e. some multifamily housing in suburban areas), mixed-use zoning (so you can walk to stores), and better public transit in suburbs. See also: https://en.wikipedia.org/wiki/Missing_middle_housing. Suburbs that have these features tend to be in high-demand, they're just rare today because they're illegal to build in many places (I think there's some commentary on that here: https://www.youtube.com/watch?v=MWsGBRdK2N0).
> they'd most likely try to move into more rural areas
Unlikely IMO because again I suspect that many/most have moved to suburbs for their careers. There aren't nearly as many jobs in rural areas.
> 15-minute city
Anyone claiming this is bad is just being disingenuous IMO. ~Nobody promoting 15 minute cities wants to force people to live in cities, they want cities where you can meet most of your needs by walking or cycling or taking public transit. If you don't want to live in a city or want to live in a city and spend 10s of thousands of dollars on a car you still can. I don't think we can extrapolate much about what the average American wants based on those who believe that conspiracy theory, because the people who believe it are either woefully uninformed about what it actually is or are just being malicious reactionaries.