Indeed, in this case, we are also aware that this is their business, but by always doing that, in fact, sometimes we think that one of the reasons the Bundesliga became a farmers' league started with conditions like this.
A little improvement in the mission maybe it could be better and indeed if they are in this case they are still doing the same thing for selling their young players but I quite agree with you at least they should think about selling to other clubs if necessary outside of the bundesliga club because it gives young talent to Bayern is the same as further strengthening their rivals.
Call it Gotze and Lewandowski, who really were a crushing blow, especially for Lewandowski, who indeed had a brilliant career at Bayern and actually destroyed Dortmund in the end.
That's what happened in the Bundesliga where Dortmund were ultimately unable to become champions because they didn't have the mental strength to become champions. As you said it is true that these two teams have always been the center of attention in the transfer window in previous seasons where Dortmund were able to accept offers from Bayern Munich for their players and this situation often occurred from these two teams even though they were rivals in the title race.
Apart from that, Dortmund have a business that they have run for several seasons where they are able to score star players and sell them to other clubs at quite high prices, like when they sold Haaland to Manchester City. thus I think dortmund will always find it difficult to break Bayern munich dominance in the bundesliga.