This season is pretty weird for Manchester United. Total failure in the Premier League and going to a Europa League final at the same time.
I can assume that the players are way more motivated to fight for a European trophy and totally not motivated to put any effort in the remaining games of the English Premier League. Tottenham was also a failure in the Premier League, but a success in the Europa League. Two things come to my mind. 1.The Premier League is very competitive. 2.The English teams playing in tournaments like Europa League and Conference League are way too stronger for their European rivals. Anyway, I would put my bet on Tottenham winning EL, mostly because they are viewed as outsiders.