Why do Democrats govern the largest cities in the US?

Why do Democrats govern the largest cities in the US?

Of the 50 largest cities in the United States, the mayor is a Democrat in 39 cities, while there are 8 Republican mayors and 3 Independent mayors (2 elected with Democratic support).

This means that 82% of the 50 largest cities are managed by Democrats.

Of the top 10 largest cities, all have Democratic mayors, the lone exception is the 9th largest city (Dallas) with a Republican mayor.

Why do you think this is?

Source: Wikipedia: List of mayors of the 50 largest cities in the United States

Why do Democrats govern the largest cities in the US?
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