Maybe it's because urban environments aren't really "nice". For all I hear about the joys of urban living, as espoused by others, I haven't enjoyed it much. Public transportation is crowded and smelly. Fat people take half of my seat (not nice to say, but I'm not sure how else to put it). Things are small, which for a taller guy like me, is pretty tough. As in, every thing is tiny. Living spaces, shops, streets. Streets often have trash strewn on them, and don't smell particularly good. I have to keep one hand on my wallet. Sometimes, hobos got aggressive. Not as much as an issue for me, but I'd hate to be a 4'9" lady. Keeping pets is hard. Cooking food is hard. I didn't have kids, but those I knew had a hard time with them. Things are very expensive. It's loud. There's a lot of traffic. Some times (all winter and some times in summer), it's bad weather for walking. I guess I shouldn't be complaining, since I at least didn't see much in the way of human feces.

This is not to say there aren't up-sides. I like the food, and there are interesting people. It's also much easier to find certain things; for instance, a few major cities still have serious "maker shops" with tons of electronic components. Smaller ones or sub-urban areas often can't accommodate them, as they are in low enough demand that serious density is required.

Maybe this is just NYC. I didn't live there a really long time, and I guess I might have gotten used to it? Still, I like sub-urban living and empty green space. I can hardly blame people for moving out, if it's viable.