It’s pretty simple – given a choice post adolescents will gravitate toward an urban lifestyle rather than the suburbs. The dating pool is larger, there’s more to do at night and everything it within walking distance. Kids don’t get up early and get out – they sleep in late, work off the hangover and spend the day preparing to go out again at night. They’re not going out during the day and the weather doesn’t mean jack to them. An urban environment fits their lifestyle better.
Plus there’s the policitcal climate.
When she grows up her priorities will change and the surburban lifestyle will beckon anew. It’ll take a few years for the novelty of being a faux-adult to wear off, but sooner or later almost everyone gets there.