I'm an aging millennial, but on a purely personal level, when I lived in a city with good public transit, I was a lot happier, most of the time. I really like stepping off the train and the bus and being on my own two feet, the walking exercise, not being chained to this thing I have to worry about. I hate driving, I hate parking, I hate owning a car--the maintenance, the ongoing cost of fuel and insurance, all of it…
I think a lot of younger people who choose to live in a city, especially new grads, are essentially continuing their college experience. A lot of friends probably live in the city too. They can often bum transportation/do joint activities from friends who do own cars and are mostly fine with minimizing out of city activities that require a car.
They also restrict themselves to jobs they can easily get to. Which in tech was basically impossible in, say, Boston 25 years ago.
A friend of mine made the observation that people mostly just don't do optional activities if they're hard or expensive to do. So if you live carless in a city with decent public transit, you mostly restrict your recreational activities and people you get together with to what's convenient and tend not to do things that require renting a car on a Friday night and returning it Sunday or Monday.