That's their business and how they earn money for their team. Maybe their first goal is to earn money and just be on top of the table to get the champions league ticket.
Been more than ten years since we didn't see Dortmund win the Bundesliga title and from what we can see they are not even trying hard for it.
Since 2000 it really belongs to Bayern Munich, only a few seasons where they failed to win the Bundesliga, and Borussia Dortmund have won the Bundesliga twice in a row when Jurgen Klopp was with them as manager after that you will only see the name Bayern Munich as Bundesliga champions, maybe Borussia Dortmund can stick with their strategy of making money and continuing to sell their best players at high prices but if they are also managed by a manager who is good at strategy then becoming a Bundesliga champion by sticking to their business style of making money can still be done, maybe by spending more money to bring in a better manager than the current one will allow them to become champions, I mean Edin Terzić is a good manager because he has led Dortmund to win the 2020-2021 DFB Cup but they need more than that.