Dortmund management focuses on certain players each season. And try hard to make these players experienced. Dortmund have a number of talented players in their squad. However, their overall squad performance is not very good. And when a Dortmund midfielder or striker joins a big club like City, Munich or Madrid, their performance becomes even stronger. The main reason for this is the strong performance of teams like Madrid and City. Their midfield and attack are also strong. This is why they get a lot of support from other team players. So naturally their performance becomes more dynamic. We see Haaland and Bellingham scoring a lot of goals.
Mainly it's because Dortmund management is more business minded than getting or winning trophies,Haland was in Dortmund and was given the attention and much needed training so as to keep his value up enough for them to make good profit from his sales which was what they achieved, so these players tend to thrive better at othe teams because at Dortmund they were training.
Mentioned it in ones of my post few days back that Dortmund has now looked like a breeding ground for good brilliant and young talent, a we have seen this play out in most of the season. Where they train players and sell them off , if some of this players were to be in Dortmund till date I think they would be stronger than Leverkusen or Munich
Currently they may be focused on some players who will be potential means to increase their pockets by the end of the season that's why how well this players shine in Dortmund isn't much of a problem to them but they make sure the players get so good enough to be marketable regardless they will still perform well by mid season and be sure to finish amongst the top five teams.
No matter how business minded the Borussia Dortmund management wants to be, they should know that Borussia Dortmund should've been one of the strongest clubs in not just in Germany but in Europe at large.
I think the club should stop the policy of always selling their best players to another club but rather they should build a strong team that'll be major contenders for German and European competition in coming years from now. We must break the deadlock