If only they had reduced the number of sales of their quality players and kept more within the club to achieve, I'm sure they would have achieved something impressive by now and maybe they could have won the Champions League for the second time. But that's them, business is business, if there is a player who has the potential to bring in a lot of money they will not hesitate to let him go, even if that player is a very scary specter and has contributed a lot to them while in the squad.
And yes that's Drotmund with all its business. Lol
We can't complain about this in Dortmund because that's how their business works in Dortmund and that's how they make money. Dortmund usually invests in younger talents and grows these players after a few seasons they will sell these players to other top teams for much more money, however, I think there are many other players who were playing for Dortmund and then Bayern Munich bought them for more money.
Dortmund football club is just following their pattern of business and that is the way that they profit in the sports business. You cannot tell them to abandon their method. In the German Bundesliga, we can attest that Bayern Munich has dominated all the trophies for more than a decade. So grooming of young players and selling them at exorbitant prices is the way that Dortmund will prosper and make their money. That was exactly what Wenger was doing in England with Arsenal because they were unable to contents with average players he needed to groom them sell them and make money for the club.