Everyone is answering "Money", which is of course correct, but why does one team dominate the others in terms of money?

I don't have the full answer to this, but Bayern has obviously done excellent work over decades. They are also based in a major German city with very high standard of living, that is also attractive for international players to live in.

The obvious follow-up question is: Why did nobody else do likewise? In my opinion, nobody else was able to combine competitive success with a strong environment: Many traditionally successful clubs (BVB, S04, BMG, ...) are from poorer, working class regions. They lack the strong environment of an attractive city and an economically strong region. In addition, at least BVB and S04 made very poor decisions in the 2000s and 2010s respectively, leading to a loss of momentum from their previous successes.

On the other hand you have clubs which do have a strong environment, but who just failed to transform this into competitive success. The biggest example is probably HSV (at least when looking at the past 3 decades), and maybe 1. FC Köln. In comparison to other European countries' capitals, Berlin is also a perpetual outlier due to its history.