I guess he wants to play in UCL with Leverkusen. Its also abit unethical to leave the club after they gave him players that he wanted but on the other hand, he is now pretty close on getting treble. One more game for Bundeslia, and finals on DFB Fokal so the last focus for his team would be on the Europa League so if he could get a treble then stay for one more season with decent result next year then pretty sure his price gonna spiked up even more
Xabi Alonso proved that he is a wise person other than his knowledge as a coach because I think leaving Leverkusen could be a wise move for him. Xabi Alonso is still young and he needs much more experience as a coach also he is still under contract with Leverkusen which can make it harder for him to leave the team and join any other team. Also, there is no guarantee that Xabi Alonso can have the same good performance in any other team after Leverkusen and maybe if he leaves Leverkusen and joins another team he fail and this is not good for him.
He needs to stay in there for a longer time and even achieve more titles with his team before leaving.
so it's useless if we hope that Xabi will move to another team, while experience is more important for Xabi.