[FrustratedMonky]

It is an interesting idea to explore: Why do humans predominantly want to live in bigger and bigger groups. Sure, there are a few people that want to live out in the country, but cities are big because people want to be there. Humans like groups.

[int_19h]

For the vast majority of city dwellers, they are there either because 1) they grew up there and that's where most of their social connections are, or 2) that's where the jobs are. The reason why cities even grew to the size in the first place is because of the economics of the Industrial Revolution - and, in some places like the USSR, deliberate policies to force the rural population into the cities to man all those factories. We don't actually know the real preferences until those factors are out of the equation.

[superturkey650]

Bigger groups of people allow for better economies of scale and allow for a wider variety of businesses and interests to be catered to.

[FrustratedMonky]

And more bars, restaurants, theaters. It isn't just economics that drive people to be together. People also like to be together, and bigger groups allow more group activities. Kind of both, in a feedback loop. Economics, jobs, and fun.