The English teams are playing under a burden of pressure. Man Utd and Spurs falling in the semis to weaker opposition would make the PL look weak. Ange and Ruben must get their teams to win.
The Europa League semi-finals this season have not started because Manchester United and Tottenham Hotspur are still in the semi-finals to make a better victory. You don't need to doubt the teams from the Premier League because they are only under pressure when playing in the Premier League, but in the Europa League both are still equally strong and have advanced to the semi-finals in such good condition.
The two EPL teams in Europa league are considered big teams. If not things changed, Manchester United is a champions league team. Tottenham Hotspur in the other hand is bigger than many teams in the Europa. Even an average English team is considered big because of the money in EPL.
Manchester United inconsistency stops in England, it doesn't affect them in the Europa league. Also the his which they made in this last meeting with Lyon has given them the confidence of lifting the title.