Overall the majority of problems stem from a lack of quality throughout the side, this leads to poor decision making, crumbling under pressure, whatever you want to call it.
Using Wharton as an example, not because he's the worst but because he comes to mind first.
Wharton is slow, he makes decisions slowly and is criminally one footed. This leads to us moving the ball out from the back ponderously, which leads to possession being heavily concentrated to one side of the pitch when he has the ball, leading to players having to play with their back to goal (predominantly right footed, receiving it on the left). Teams squeeze up, our players move over to condense the play and try to get numerical superiority, we make mistakes and the compounding impact multiplies over a phase of pay with players being out of position to cover mistakes. They switch the play and we're caught out time and time again.
You could replicate this model across the pitch where individual deficiencies cause massive problems that lead to a disjointed unit that when playing anything other than trench football, with 11 men behind the ball struggles.