Bayern is a very wealthy club with a very sound financial policy. Basically, they can keep any players they want. They also don't let players go easily. Lewandowsky did leave last season, but that must also have had to do with his age. They handled that reasonably well with Mane. And Sane has also come over for that from Manchester City. I don't know if they plan to get more players, but they already got de Ligt in the summer, which was also a good reinforcement. It doesn't matter who they play with, the B team is also so good that they easily become champions.
If Dortmund had adopted the style of Bayern Munich they would have been doing well and also be a rival to Bayern Munich. Bayern Munich don't easily let their good players go until they have a good player that can be a Replacement unlike Dortmund. Dortmund sells their players their important player's even without having a play that can be a Replacement. Bayern style of management is quite different from that of every other club that is why winning the Bundesliga league is easy for them unlike other teams.
Do you think Borussia Dortmund has the potential to adopt the style of Bayern Munich in the near future? if I don't think so. Although in the future they could do it, but in the near future they do that I don't see that possibility. I also have the same thought as you, that if Borussia Dortmund don't always sell players with potential, then I really believe they will be at the level that Bayern Munich is now. However, the reality is the opposite, that is, they only make a profit from selling their players.