More precisely, Xabi Alonso is currently being targeted by many of Europe's top teams because of Xabi Alonso's success in creating or building the Leverkusen team as it is today.
It's true that many clubs currently have him as their preferred candidate, but he doesn't have an exit clause for any clubs other than the ones he played for as a player. He would therefore have to fulfill his contract until 2026 or a high transfer fee would have to be paid for him. It's questionable whether clubs will do that if there are alternatives.