We already knew he was going to leave Bayern Munich. Tuchel joined Bayern Munich to help this team have better performance during the Champions League because of the experience he had in Chelsea the Champions League and that is why they used this coach. But the fact about Tuche was about the bad performance he had in Bayern Munich made them lose the Bundesliga title after ten years of winning it.
On the other hand, Tuchel had a bad relationship with many players in Bayern Munich and this made Bayern Muhch to stop working with this coach.
Winning Champions League is not easy and we can see how long Real Madrid waited to win their Decima, the tenth Champions League title. It takes Real Madrid 11 years to get only one more Champions League title, from 2001 - 2002 season to 2013 - 2014 season. Tuchel could do his job bad and not as good as Bayern Munich expected from him but they must be realistic too, it's not easy to win Champions League.
List of Real Madrid's Champions League titles.
They possibly made a good decision to stop working with Tuchel because with his bad relationship with many players, it's hard for him to work with these players and improve Bayern Munich performances next season.