They don't have much choice because even if Ten Hag is replaced as coach in the end they can't be sure whether it will be a good change or not to make considering there is no guarantee for the new coach to shine and get the same trophy as Ten Hag did when coaching.

We have seen from this decade alone Manchester United have made a lot of coach changes but only a few can provide trophies for them at the end of the season.
This may be another consideration for Ten Hag to be retained.

Although in this case I also don't really like why he continues to be defended but I think Manchester United also know that this decision although heavy but must be done with some considerations that they realize there is actually nothing easy in terms of the risks that must be borne.