Leverkusen lost so many top players, and expecting a new coach to improve their performance isn't enough, especially with their current lineup being so-so. However, since the Fiendly Matches, Ten Hag hasn't been able to improve the club much, and even after the Bundesliga season, Leverkusen hasn't seen significant progress under Ten Hag. Ten Hag's habit of expecting more time to adapt to the club seems to be unacceptable at Leverkusen, a stark contrast to Manchester United. Therefore, he seems quite surprised by this dismissal. However, at least it could be a positive move for Leverkusen.
Now everyone can say that Ten Hag isn't the best coach to fix a team, and that was evident after he was fired at Manchester United and returned to Leverkusen as head coach. The team has had many problems since the departure of Xabi Alonso, and the departure of several key players last season will only exacerbate the problems. Adaptation is always an excuse and the time needed will not be enough to change Leverkusen for the better this season so considering bringing in the former Dortmund coach is much better because he understands Bundesliga football better than Ten Hag.