I suspect there are regional differences that matter as much or more as size does. A 200K city in Europe that's a short train ride from a larger city is going to feel very different from one in the southern USA with no easy connection to a metropolis or one in the west that's kind of sprawling connection of similarly-sized cities, which adds up to a large city, but over many square miles.

Job is definitely one of the most common motivators, but a lot of people are drawn to aspects of the "character" of a location, which is more some mix of common habits, popular amenities, and other social expectations which make your life and interaction styles seem more or less weird than other places.