Because Manchester United did not manage to finish in fourth place in the English Premier League, which is known as the tightest league. They finished fifth last season so they have to play in the UEFA Europa League. That's the answer.
Manchester United's overall good performance against FC Sheriff was not only on Cristiano Ronaldo, there were several other players who had a big role behind Manchester United's victory such as Diogo Dalot, Cristian Eriksen, Bruno Fernandes and Casemiro.
The fullbacks contribution to wide attacking play this season has impressed me as the most improved part of Manchester United. The crosses and passes give Manchester United assault a new element that wasn't present before Eric Ten Hag. There is still opportunity for improvement in the offensive play from central midfield, which Casemiro's presence will hopefully address. The team still needs to improve its finishing up front.
Manchester united have what it takes to lift the Europa league title this season, afterall they're in form and their coach, Erik ten hag knows how to deal with average teams. Cristiano Ronaldo have gained back his confidence in scoring goals after he net a goal in last night game and did the peace of mind celebration. It's worth celebrating to see him back on the pitch after suspension from the board. United have engine room of Midfielders who did the tackling and interception of the ball and also creative ones at that, the reds devil's needs to win games inother to proof to their fans that they're still strong as before.
Ronaldo is still Ronaldo. He just needs to recover mentally. He does it slowly, despite the outside factors. I have no doubt that he will come back if he breaks the pressure and gets the time and respect he deserves in the team again. Besides, every sane football fan knows what "Instigating Ronaldo" can do. Ronaldo's biggest problem is that because he is away from the fields, he wants a pass in every match and even leaves his own position to touch the ball and enters the bottom of the offensive midfield. This guy really missed the ball, it's a very childish longing, I realize that, so it's wrong for him to leave his position, go all the way into the midfield to get a pass. If he does not want to be a striker, he can state that, which we know he does, but he should not run out of the task given by his coach just to get the ball. The man is over aged. He is not a young forward who has enough energy to return to his position. With Ronaldo like this, and the overall performance of ManU, I don't think they are a big contender in this league. The teams that will come from the CL will have a higher chance for the title, in my opinion.