> and the idea was you needed to live in the city to do it.

Exactly. Humans crave novelty and hate doing what everyone else is doing. That idea was presented because it was still a fairly novel experience to live in the city. Getting to live in the city was seen as something special. Now it is what everyone does, so it isn't novel anymore. You no longer "need to live in the city" because, generally, you are now already there. The novelty is gone. The happy youth have moved on to living the next big thing. Once everyone else starts to recognize what they are doing, general happiness will temporarily increase again... until that new normal loses its novelty and the cycle repeats once more.

It is the tale as old as time. This is ultimately the same reason for why people set out to discover and settle in America in the first place!