I can't say whether this is because Manchester United don't want to rush into making a decision and are trying to keep their current coach despite the performance we can see for ourselves or whether there are other factors that made them decide to keep Erik Ten Hag. Because it could be that they retain a coach because the coach is considered to "comply" with what management wants, or in other words the coach does not demand much and so on.
I just want to think positively about their decision now because they don't want to rush, because even if they fire Erik Ten Hag there is no guarantee that they will be better. Apart from that, maybe they appreciate it because at least they managed to become champions in the FA Cup and allowed them to play in Europe, even though it was only the European League, not the Champions League, because they managed to get a ticket by winning the FA CUP.
Manchester United is most luckiness of Premier League teams get participants in Europe League after winning FA Cup regarding failed reach the Europe League spot standings place after finish on 8th position.
Have the same manager under Erik ten Hag and will Manchester United get success achievement regarding last season failure in Champion League group stage as the most bottom standings position team.
Currently, Manchester United have bad performed in European competition not only with UEFA Champion League but also in Europe League, I don't think they can't reach until final phase for next season behind many top teams are qualified to Champion League but get possibility with the relegated teams from UCL become difficult opponent team if Manchester United get qualified from group phase.