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.
It is not only because Bellingham played well in the previous season but Real Madrid has many good midfielders as well. It is impossible to replace Kroos with another player who has the same play style, Ancelotti only has some options that can replace the role of Kroos in the midfield line. When Kroos decided to retire, surely Real Madrid lost a very crucial player. However, Ancelotti must find out the solution to deal with the lose of Kroos. With the current midfilders, Ancelotti should be capable to deal with this problem.
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.
It is true that Kroos didn't score many goals, but he made a lot of assists. Kroos also has a crucial role in the midfield line, whether in defending and in attacking. Sure, he has the capability to stabilize the midfield line of Real Madrid. It is very rare to have a player like Toni Kroos. I'm not sure if Bellingham can replace totally the role of Toni Kroos. In the previous season, Bellingham tends to play as an attacker. He isn't a typical player who functions as a team balancer in the midfield line. I prefer Valverde or Camavinga, to replace the role of Toni Kroos.