Over the years that's what Dortmund always do and are excellent on it. So many players improved in Dortmund then moved to other top clubs for millions, making Dortmund richer and giving them funds to search for other players to start again.
Selling Haaland was quite interesting last year and people thought that Dortmund was doomed but they played very well and were able to almost get the first rank but they failed at the end.
Because they never stop, after selling a player they know who to replace him and how to make him a star, that top clubs want to buy. Dortmund is the kind of team where the players are always in the spotlight because everyone knows that this team knows how to find great players. The players also know this and try to show their best, because each of them has a chance to go to a big team and get a great contract.
Thus, if there are Dortmund players who choose to be loyal to Dortmund for the long term and reject offers from other big clubs then that is the wrong choice. Sorry, an example like Marco Reus. Because after all, in the end it is difficult for these players to be able to win titles and or trophies, because Dortmund is not a team that focuses on winning titles. But yes, even though Dortmund only focus on producing great players and profits in sales but yes, when Dortmund has the chance to win the title then of course Dortmund will also try hard and the example is like this season for example.