[skybrian]

It sounds like positive feedback loop. Some reason (usually jobs) results in higher density, which results in a shortage of housing and higher prices, and that’s an incentive to build denser housing so that more people can move in. The available workforce might attract more employers, and the loop continues.

You might as well ask how cities get started and grow larger. Contrast with farmers.

A positive feedback effect will keep going until there’s negative feedback counteracting it. That’s almost tautological. The specifics will be more interesting.