Obviously, These Football clubs are not just there for entertainment 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.
Nowadays football is an industry, so a club would be better if it had a good business and was able to generate a large source of income. Dortmund have done that, so a lot of good players have left. This also resulted in disappointed fans. Because indeed the orientation of the club looks different. They don't have many trophies but their finances are healthy. Of course this will make the club not have much burden to pay players, although they must be willing to rarely have trophies.