They can do that. But people who live 15 minutes from downtown also want to have less density where they live --- most homeowners would! --- and that is a problem.
You just said increased density isn't a problem for families and then describe people wanting less density a problem. If it's a problem for society that families want less density, then it's a problem for families if society want more density.
I don't believe it is a problem, but people can have preferences for things that don't rise to the level of public policy problems, and if they'd prefer to live out in the country, God bless them.
A lack of density closer to cities is a real problem: it makes living close to where you work prohibitively expensive, and promotes sprawl.
