Everyone dreams of big cities. It's not just foreigners longing for the Federation's big cities; people from small cities within the Federation also yearn for big cities.
Many people dream their whole lives of living in a big city, having a small place of their own, and being able to identify as big city folks. It's their lifelong goal.
Thus, we see many small cities experiencing a population siphon effect from surrounding big cities, with young people scarce in these cities.
Valley City used to be like this, with Golden Port City nearby, a city full of opportunities and wealth. Almost any young person with a bit of ability would head to Golden Port City in search of opportunities after graduating high school.
If Valley City hadn't become the "city of film," its population loss would have become more severe.
