And when you think about it, if Dortmund's main objective is to make money, winning the bundesliga could also bring financial benefits. On top of that, if the club kept its best players, they could pursue additional rewards in prestigious competitions like the UCL. Unfortunately, Dortmund seem to prefer the immediate profits that come from selling their players.
For Dortmund to win the Bundesliga, the club would have to spend a lot of money on expensive new signings, and the title wouldn't be guaranteed because they would have to fight against Bayern, who dominate the league. So they'll spend a lot of money to fight for the title, and after that, they won't win it. They'll have less profit than with their current system of acquiring new talent at very low prices and selling them for high prices, finishing in the top 3 and securing a place in the European Champions League, which gives them money for qualifying. It's a lucrative business for them; they don't spend much and continue to profit.