That's because young people don't have families.

You see this play out with every generation. I read an article recently that incredulously reported that Millenials - the car rejecting generation! - have started buying cars. Of course they have, because they're coming into the age where they get married, have kids and move to the suburbs.

So, you're right, in that this is a young/old split. But don't expect it to persist as the young become old.

EDIT: the more I think about it, the more interested I'll be to see if there is, in fact, a trend in the opposite direction. The suburbs are a total compromise - close to job centers, retail facilities, etc etc, while far enough from city centers to be affordable. The coming era of remote work and efficient delivery services might mean that living further away from the city makes more sense. But there are a lot of caveats in that.