If judged from achievements in the Premier League, Ten Hag has failed to make Manchester United a club that is ready to compete in the top four, so there is no reason for Manchester United to continue working with Ten Hag.
I respect your thinking but I don't want to be unfair to Erik ten Hag honestly. Let's take the last season as an example. Manchester United faced a huge injury problem. So many important players were absent for a long time which affected their performance directly. I don't think this is a bad excuse. Every team would have serious difficulties in such condition.
Their defense was affected the most by this. They conceded too many goals. Even when Varane returned from injury he couldn't perform decently. We didn't even see Lisandro Martinez being able to play properly either.