What caused the "urban revitalization"? Was it just that people who hadn't been around during the 1968-~1980 urban hell were finally in a position to be buying their first homes?
You can see this happen in many ways aside from city's becoming safer: Real estate cost increases in cities, The whole bike-movement is an element of it, NYU getting 44k applications, the growth of the Brooklyn "brand".
I think, generally, there's a real desire for an urban community with culture and shared experiences. I know I don't have anything more 'concrete' to back this up, but this is the general sentiment of my friends (in their late 20s to early 30s.)