It's a good one they want to make a change of their coach but it could be that's not allthat it is to their issue of poor performance and productivity, although they have not explored their policy of selling of their best players too often recently but then it's possible the long term after effect is dawn on them now and they are looking to explore options to fix the team, mea while a build up all over again is what I think will be best for them currently. Good thing is they can afford a good coach if they get one.
They have to change the pattern and may not sell some important players even though the price offered is high. Changing the coach is also not fully successful because sometimes this will actually make the conditions worse. They need to rebuild the team to be stronger and do not necessarily sell every player who shows an increase in performance for reasons of profit. If you want to rebuild the team to be stronger then it takes time because it is not easy to achieve success in a short time.
source
Some talented players sold by Borussia Dortmund, I imagine if they prefer to keep them, then I think they will achieve great success.
Even if they are currently experiencing a very deep decline, I am not surprised by this, because previously I also predicted that something like this could happen at any time. Keep in mind that even though they are very good at finding potential young players, sometimes they are not lucky enough. They can't regret it, what they have to do is change what they have been doing.
Maybe you are talking about Dortmund players being sold and you think the bad results in this team are related to this and since Dortmund selling players they can never have good performances in the Bundesliga games. But the fact about Dortmund is that's not something new about this team and they have been putting the superstar players for sale for a long time, that's how their business works in this team.
Not having players like Erling Haaland and Jude Bellingham was definitely effective in Dortmund but that's now something new and I think the main problem for them was about their coach because since they started working with Nuri Sahin. Now since they got their coach fired maybe we can hope to see better results from this team if they get a better coach in Dortmund.