You are right and all people in Germany know how they work in Dortmund. They usually pay attention to earning money for their team by selling young players instead of buying expensive players while all other teams usually try to buy these superstar players. Jude Bellingham and Haaland are two examples they were both playing Dortmund and they left this team while Dortmund could earn a huge amount of money from these two players.
Also, Dortmund got many fans and they are one of the most popular teams in the world and they can use this potential and fans for their team.
But after all these, Dortmund was not successful in wining trophies because their first priority is earning money for their business.
Thats not fully true , Jude Bellingham and Haaland and also Lewandoski was sold because Dortmund could not afford their salary.
The salary is mostly the case why they got sold , what brings you 3 Star Players that cost you huge money.
For sure Dortmund would be stupid for not getting money back from all this players when they get to another club.
Sad that they lately not have won trophies , but at some stage thsi time comes.