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.