I think they may have decided to keep him in the team because they couldn't find a better candidate to replace Tuchel. Kimmich is an important player, but if Tuchel remains in the team and is determined to leave, Bayern will lose an important player. He is an important name for Bayern at the age of 29 and can make important contributions to Barcelona if he joins them.
Perhaps this was a decision that the Bayern München management was forced to take, because due to time constraints, they had no other choice to replace Tuchel as Bayern München coach. Kimmich does play a very important role in Bayern München's attack power, but he must restrain his ego for now and must remain at Bayern München, if Tuchel is retained. It is indeed very difficult for Bayern München if they have to choose between 2 options like this, so it will be a big problem for Bayern München in the future. In my opinion, things like this really need to be rethought by Bayern München's management so that it doesn't have a too bad impact on the quality of Bayern München's play next season.
If Tuchel stays, I think he will do a lot better next season, I know that he didn't do so well, and he is the manager of the team that lost for the first time in over a decade, so it does look like they do not want to keep him. But looking at the situation right now, with some good summer transfers, he should be able to build a team that will go great next season.
Plus, I really do not think that Leverkusen will be able to do the same success next season, look at how Napoli was the winner last year and barely getting any wins this year, same could happen to Leverkusen, they could just lose some great players, fail to replace them, and be a mediocre team next season again. This is why I see chances of Bayern higher, with or without Tuchel.