How did Bayern get so rich?

For reference, I'm new to the Bundesliga (go BVB 😄). According to transfermarkt, FCB is twice as rich as BVB, the second richest team, who is only twice as rich as the fifth biggest team. I was wondering when this spread first formed and how? Given FCB has won the league 15 of the past 20 seasons (including 10 in a row), I'm assuming this spread has been the case for a while now. Can anyone educate me a bit on how this situation developed? It seems to me that as far as the title race is concerned, the league has become quite one-sided and I suspect this is in part (largely?) due to the difference in resources available to FCB vs everyone else. Am I wrong in that assessment?

P.S. Please don't be hostile with me, I'm not angry or anything, just honestly curious