If Haaland moves to Bayern Munich, it's going to be crazy to say the least, how many times will it continue to happen that way, and if it does happen in Haaland's case, then that will connote another ten years or so dominance from Bayern Munich, that's absolutely not what football fans want to see, except Bayern fans of course, but I mean, football is all about competition, that's the fun of it all, if one team continually wins the league without anyone pushing them to their limits, then it somewhat reduces the importance of the league title, and they'll also somewhat lose viewers, of Dortmund are going to sell Haaland, then let them sell him to a non-German club, that way they aren't directly weakening themselves, to strengthen a direct opposition.
Other teams can be like them when they sell their players to them, nobody want to weaken Bayern, all football fans want is a competitive league, that's all.