Yeah Dortmund could have been even the strongest team in the Bundesliga and a huge threat in the Champions League every year as well. But they didn't keep nearly all of these players here.

The explanation for it is simple. This is their policy. They bring young talents, these players grow and then they get offers from bigger teams. Dortmund doesn't refrain from selling them by a big profit.

Some of them went because of a release clause though otherwise they could have made even bigger profits from those players (such as Haaland).    Dortmund don't win titles much but they still make huge sum of money thanks to player sales.