There is nothing wrong with doing business in the football industry and that is what they do to make a profit. If the business is run like the one run by the owner of Dortmund, they will never achieve the club's achievements. The reason is that they only focus on selling players and never try to buy quality players at high prices. A trophy is a big hope for any club, but if the club does not have a supporting force of quality players then it will be difficult for them to achieve it.
Obviously, These Football clubs are not just there for entertainment's sake but are also for their business dealings and I do believe this is why Dortmund sold this incredible player at some point, fast forward back to when Arsene Wenger was in Arsenal as the head coach, this was a kind of business Arsenal football club was into, grooming of players and selling them when they are at their best to raise money for the club.
Are you aware, that even though Dortmund always sells talented players, in reality, Dortmund is still capable and/or successful in becoming a team that can compete well in the title race every season? Last season Dortmund almost won the Bundesliga title, but Dortmund again and again had bad luck in the last match of last season. So yes, even though Dortmund prioritizes business and profits, the reality is that Dortmund still has very good management to remain a title-challenging team every season and that is of course great I guess.
I agree with you, this is the angle at which the club should equally focus or pay more attention to, while they do business as usual selling those key players, they should also ensure that the club is still living up to their expectations by winning trophies without the club feeling of the negative impacts in term of the player departure affecting the overall performance of the team because of their contribution to the team.