I agree that Ten Hag's performance was disappointing and he couldn't get the results they wanted to see from him during the time when he was working in Manchester United during this season and this made the fans of Manchester United agree to say the team gets him fired.
But we can't forget that in the last season when Manchester United had a bad situation and they tried to hire some other coaches, in the end, Ten Hag saved the team and he had a good performance regardless of him starting working in Manchester United in the middle of the season.
regarding the results obtained Ten Hag last season, it was indeed very sad and many people were very disappointed, but if you look deeper, Man United actually experienced many problems which forced Ten Hag to try to improve everything even though the results were bad, but all of that is understandable because many players are injuries and new players who don't meet Ten Hag wishes or in other words new players who can't make their best contribution.
there may be several reasons why Ten Hag was retained at Man Untied, but the main one may be because Man United still gives Ten Hag the trust and opportunity to fix all the bad things in the previous season.
all of this belief emerged after remembering, as you said, that Man United was saved by Ten Hag and managed to finish in the best position in the EPL standings and until now this belief is still given by Ten Hag, but after this season, if the results are still the same, it looks like Ten Hag will be replaced by a new coach.
next season will be the last season for Ten Hag to manage Man United and if Ten Hag wants to stay longer with the Red Devils, he has to fix everything in one season.