I think it is a case of Kane and his terrible agent not really doing their homework before this move. Bayern were very lucky to win the league last year and only did because Dortmund bottled it on the last day, there were already rumblings of discontent with Tuchel last season and at the same time many were admiring Alonso and felt Leverkusen were ready for something big. With Alonso staying at Leverkusen Bayern will have to invest heavily this summer, they will also most probably lose Davies and Kimmich and are stuck with Dier. In hindsight i think Kane may wish he had seen out his contract at Spurs