Watch closely. Locatelli marks Sampdoria's attacker instead of the attacker marking Locatelli.
As a regista you need constant movement back and forth, vertical and orizontal always looking to receive a pass, always moving where there is space, relieving the pressure off of fullbacks and cb's, but Locatelli just positions himself behind Sampdoria's attacker and practically takes himself out of the game.
I don't know if Allegri sees this or not, but he clearly is down to the player not knowing how to play the position or Allegri's instructions.
It could also be that the player is lazy because doing that, means you have to have great stamina.
That's why Pjanic was always one of the players that runned the most for us.