Normally football is a way of making money which I believe each club will find a way of getting profit from it, club that are at the top like Bayern Munich that always win their Bundesliga title, they can be blamed because they no the path, maybe they notice selling of players is most than trophy.
No doubts the main purpose of everything at the end of the day is to make profits and every team wants to achieve that regardless of how it's been achieved, because they need the profit the run the team and also keep their owners in business, so if they are not making profits enough then their owners may be forced to sell them off or take measures.
As a result of aiming to get profit, various teams have device a means or a strategy to achieve the said target. Some teams achieve it by getting to win more trophies, such as Bayern Munich in the bundesliga and Manchester city in the English league. While others may want to use the sales of players to get their own profit as seen with Dortmund, which ever way that best fits the team, they adopt.
For teams who achieve theirs by winning trophies, you see they invest so much in buying players and transfer to build strong team enough to get them the trophies, while teams who gain from sales of players, invest so much in training and coaching so they get solid players who could be marketable, and their target are usually young players with talent because they seem to have better Market value.