Some of it may be the previous generation's "American Dream" (I won't call it false, because it wasn't for them or for many of us whose parents lived it).

A lot may also be attributed to getting older and wanting to slow down, start a family, etc. Just ask any parent how much they enjoy SF's school lottery, or inability to let their kids play unsupervised outside for safety reasons, or lack of a back yard.

Having lived in a city most of my life, lived somewhere in walking distance of Mountain View, and now live somewhere in the Peninsula that I need to drive from if I want to get anywhere of note, there are definitely tradeoffs. It isn't always black and white. I miss the walkability, but I also love some of the other features of being more removed from the congestion and city centers.