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I think we should not forget where Borussia Dortmund is coming from. In the late 1990s and the early 2000s they were at the same level as Bayern Munich or maybe even ahead of them a few times. In order to do that they had to make very high debts though which almost led them into bankruptcy afterwards. Then Jürgen Klopp came and the club has risen again and they even made it into the Champions League final back in 2013. Still they are pretty far behind Bayern in terms of financials.
A little flashback to the history of Dortmund. if I'm not mistaken, Dortmund is one of the most successful clubs in Germany with a score of 8 German league titles, only losing to Bayern Munich. they have also won the Champions League trophy once.
The 90s were the golden age of Dortmund, and in the 200s Dortmund became the first German club to open publicly or go public. they won the Bundesliga trophy in 2002 and were runners up in the UEFA Cup in the same year. but after that they experienced a drastic setback, financial problems again became the cause. debt that many make Dortmund have to look for loans so as not to go bankrupt. in short, Dortmund was given a loan by rival Bayern Munich.
During the Jurgen Klopp era, Dortmund's achievements immediately increased. in short, Klopp's arrival made Dormund excel again. well, as you said Dortmund is far behind Bayern in financial terms. that's why, they changed their business style to create more young talents to become stars and then they sell. that way, Dortmund does not rely on ticket sales and sponsors. and now, they are one of the clubs that always generate high profits. Naturally, if their current priority is not focused on the trophy.