You could see from Amazon documentary that Alli was vocal in his objection to hoofing the ball long and failure to retain possession. I suspect this has not been lost on Mourinho. I doubt whether this is the sole reason, but I'm sure Alli has questioned his tactics on more than one occasion
Think it was Rose who said something about passing it sideways in defence then goalkeeper hoofing it, but Alli’s outburst where he was called out by Dier shows him to be a bit of a spoilt brat. If he showed as much desire and aggression on the pitch he would be back to his best. The best players perform consistently on the pitch and earn the right to bust balls in the dressing room.