Every club has its own way of managing its team, they know what to do especially in business to get profits and one of them as usual they utilize from player sales. We can see how Dortmund now, they are always consistent in their business, have the ability to form players who were originally ordinary to be extraordinary then they will sell them at fantastic prices even to their own rivals.
But in my opinion in general they also cannot if they continue to focus on the benefits of selling players, because obviously if it is done very often then maybe they will find it difficult to balance the team's performance in each competition because they are busy with taking care of the entry and exit of players, and also of course adaptation which is a serious problem when they are struggling to win trophies or other victories.
I do not think that football is there to make "profit", it is there to increase the value of the team for the owners, but not make a profit, you spend money to increase the value. Lets assume that you have a smaller club that worths 100 million, these days very rarely top teams worth that, but lets assume that you have a smaller one, barely relegating or not even in this league.
You end up spending 25 million euro on that club this year, so suddenly you are down 25 million, but if you club is now worth 150 million, that means you have made a profit, turned a 100 million club to 150 million club by spending just 25 million and that extra 25 million is your profit. This is why many celebs and rich people are buying teams, they want to spend money but gain more on the value. If you buy United for 8 billion, and they have no debt, no issues, you own 100% of the club, and you spent 1 billion on transfers, that means 9 billion total spent, but the club is now worth 10 billion? That means you made 1 billion in profit.