The question that arises when they do that is how long will they do it? The risk will always be there, and even though they alwasy make a profit every season from the sales they make, the question is whether they will always be in a state where they will always be able to benefit from the star players they create? I have no doubt that they are the club with the most genius in spotting young talent. But risks must also be taken, because they also need titles as a club. They have the ability to do that, it's just a matter of how they intend to do it.
Maybe they're comfortable in gaining financially from their player sales than winning trophies, cause if the trophies were important to them, then I don't see why they'll decide to sell players that are capable of winning titles for them, if you noticed their performance last season when they had Jude Bellingham in the team is not the same this season, they almost won the Bundesliga when he was present in the team, and he's now performing well at Madrid, I believe if he was still with them they would had been doing better.
What I feel is that it's become a tradition for them and it may continue for a long time, they'll still try as much as possible to qualify for the Champions League and sell some youngsters that are currently in the team, maybe Karim Adeyemi might be the next Youngster to be sold by Dortmund, but where it could start affecting them is when they fail to find a better replacement for the players they're selling.