Indeed Dortmund is synonymous with selling star players which they do in every transfer market, even this season they have done it again by selling Bellingham to another club. One of the factors that made them like this is a financial problem because they get a lot of profit from the work they do which sells players at quite high prices to other teams. I don't think Dortmund will be able to give many surprises in every season in the Bundesliga because they are not too strong to compete with Bayern Munich.
This is dortmund's strategy.
It seems like that dortmund has a reason why it was doing the strategy to buy cheap and sell high. In my opinion if dortmund is not as rich as bayern. it can become a sense reason why dortmund was doing it. Dortmund has so many reasons to explain it.
I do believe if the management has a reason why dortmund was doing such strategy and that's pretty much the same like what already done in the past. Arsenal has not owned by rich owner.
That's why the club was doing such strategy to make sure its financial is always stable.