They're probably all aware that the majority of them aren't capable of playing football the way he wants to, and are frustrated that he insists on playing like Barcelona with certain players who, when the ball is at their feet, couldn't look out of place at Barnsley.
Now, imagine you're in that squad... you know you're not good enough for quick intricate passes but your manager refuses to admit it and keeps demanding you play that way, even after you make mistake after mistake after mistake; you're hardly going to be buzzing about it are you?
Imagine you're a talented footballer like Barkley or Mirallas, and the boss is telling you to pass the ball backwards from set pieces in dangerous positions.
Imagine you're Lukaku and the boss refuses to play your best playmaker, Barkley, in the correct position and one that suits you as a goalscorer, you'd be fuming and literally soul destroyed to see Steven Naismith in that position.
Imagine you're in the starting XI and you see Jagielka, Distin, Howard starting games, you'd be virtually defeated before you stepped onto the pitch knowing that the opposition have basically been gifted a goal already.
It's no surprise it is that the players look dejected and not arsed.