Bayern Munich is the richest and most powerful team in the Bundesliga. They spend a lot of money to form squads. The squad has a lot of talented and star players. On the other hand, the other teams in the Bundesliga are not interested in spending a lot of money. And this is why we see Bayern Munich's dominance in the Bundesliga every season. In addition, teams like Dortmund or Union Berlin have not been able to fight for the title due to a lack of consistency in the Bundesliga. Compared to Munich, they are far behind.
Dortmund would have just been Bayern Munich, Dortmund is a rich club that can buy good players and are capable of building players but Dortmund sells their good players instead of keeping their players to win trophies.