Dortmund is in business to maintain the team's existence. Greed for money is necessary. We see them doing business to make a profit for the club. And they cannot retain players when the club's reputation and salary are not as high as big clubs. Selling when the price is high is a good choice for the club and the players.
I still hope big sponsors see the team's potential and are willing to invest in them. Dortmund will not be forced to sell their star.