Toni Kroos did not leave Real Madrid but Real Madrid did not extend his contract. In the few matches that Toni Kroos hasn't been on the field, Real Madrid have seen a clear weakness in the midfield. Real Madrid's current situation Real Madrid's midfield will be weakened next season when Luka Modric leaves Real Madrid. Toni Kroos was Real Madrid's best performer and was the best player until the last match he played. Real Madrid could have extended his contract for another season or two if he wanted. Real Madrid may have planned to release Toni Kroos so that Jude Bellingham can play in place of Toni Kroos and Mbappe is in the striker position. But now the problem is with the injuries of some important players. If the injury problem is solved, maybe Real Madrid will return to the best performance.
Bellingham performed well last season. Perhaps this is why the Real Madrid management does not consider it necessary to keep Toni Kross with the squad by paying high wages. Toni Korss wants to end his career with Real Madrid. So he did not join any other club. But if the Real Madrid management had extended the contract with Kross, we might have seen Toni Kross stay with Madrid.
Toni Kroos didn't score many goals or assists. But Kross is a fantastic player. He played the most important role in stabilizing Madrid's midfield. And since Bellingham is not in the squad this season. So the weakness of Madrid's midfield is very well understood. Toni Kroos was what Madrid needed right now. However, if Bellingham returns from injury it looks like we could see a stable Madrid midfield.