That's all because Sadio Mane wasn't very good last season, such as not contributing too much to Bayern Munich and this is one of Munich's policies to sell players who don't have a good contribution and replace them with better players.
I see the rumors that we talked about a few times before that Sadio Mane can't seem to decide where to go unless he accepts the highest bid from a Saudi Arabian club.
If I were Sadio Mane I would probably accept the offer because he is a bit older and without strong talent only Saudi Arabian clubs are willing to buy at the highest price.
Actually Sadio Mane is an experienced player and also has talent, it's just that last season he was also hindered by injury so it seemed he didn't contribute more to the Bayern Munich team. Apart from that, the age of Sadio Mane himself could also be a factor for Bayern Munich to sell Sadio Mane this summer because Bayern Munich is in need of younger players to compete with their rivals next season. So that Bayern Munich also needs to find a replacement for Sadio Mane even before Sadio Mane is sold.