Bayern Munich is a team that consistently retains talented players who are already comfortable with them. Therefore, Bayern Munich is always favored by many fans because the team isn't solely focused on financial gain but is also serious about fighting for the Bundesliga title. The other two teams you mentioned clearly prioritize financial gain through player sales, so they aren't favorites to win the title. But I want them to surprise with a fierce battle next season to make the Bundesliga competition even more exciting and challenging.
Bayern Munich is a club that's financially buoyant, and their goal is to challenge in any competition they will play and win trophies, so for them to achieve this, they need to retain their talented players. Bayern Munich will continue to win the Bundesliga title because other clubs in the Bundesliga don't have the squad depth to rival Bayern Munich in the Bundesliga league, and even when they have a good squad to rival Bayern Munich, they will still sell their best players to other clubs since they prioritise selling their best players for money.
Nearly every league faces similar problems, as financial issues force players to sell. No player is truly unattractive when receiving offers from other elite teams, as every player dreams of playing for an elite team and winning numerous trophies. Elite teams, on the other hand, are financially strong, so players are happy to stay, and clubs don't sell unless they can no longer contribute.
What's happening with Leverkusen right now, selling key players, is certainly a common occurrence with other teams. Dortmund, in particular, frequently sells players to elite teams, even to their rivals, Bayern Munich. This is one reason why Bayern Munich remains dominant, partly due to their financial strength.