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.
yes, you are right. Dortmund always educates players to be stronger and have great performances.
therefore it is not surprising that the players sold from Dortmund always give good performance in other teams like Haaland. and on the one hand, of course, Dortmund will not be careless in selling the best players, but they have also planned which new players to buy to be able to bring Dortmund to be strong again.
so that in terms of this transfer, Dortmund has always planned what to do to welcome the new season later.