It's not like that, they just fail because of mistakes they didn't want to make. Basically all teams will fight for the opportunity to qualify for the round of 16 no matter how tough the opponent they face, but Manchester United failed to do so even though they shouldn't have been this bad.
They really want to stay in Champions League and they have many star players who want to go far in Champions League. They are trying to go to knock out phases but their defense system is too weak to defend advantage they created from attacking. It happened in some matches with Copenhagen and Galatasaray.
Galatasaray, Copenhagen are two teams that can be said to be no better than Manchester United, but the fact is that both teams were able to give their best because of their players' performance and good use of opportunities.
Those teams are not too strong and are not big names in Champions League. Time when Galatasaray always brought fear to big clubs in Europe when they played at home stadium is many years ago. It seems they are coming back this season but they are still less powerful than they were like 20 years ago.
The match against Bayern Munich will be the last match for Manchester United to stay in Europe. I admit it was a very difficult match for Manchester United, but none of us can be sure what the final score of the match will be. Moreover, we also cannot be sure what will happen in the Copenhagen vs Galatasaray match, so there is still a possibility for Manchester United to qualify for the round of 16 by beating Bayern Munich and hoping that Copenhagen and Galatasaray play out a draw.
It is their last hope but Manchester United need double conditions and I think their chance to get both conditions, beating Bayern Munich and Galatasaray will only have a draw in match against Copenhagen, is very small. They will have to be ready for a bad ending in this group and be ready for play-offs with clubs in Europa League.