It mostly depends on stable borders and a culture of centralization. Some US states such California and Texas have multiple major cities. Germany and the surrounding areas were historically fragmented, leading to many regions having multiple mid-tier cities instead of a single dominant city.
I've heard that the book Cities and the Wealth of Nations [0] might talk about this more. I've been meaning to read it.
[0] https://www.astralcodexten.com/p/your-book-review-cities-and...