He's often not on his toes for this kind of opening, but he's not the only defender who does this. The difference is that other defenders at top clubs can move their feet quickly and get across to cover the mistake, or at least make a genuine challenge. If you put De Ligt or Demiral in this position and asked them to cover there is a chance that they will get across to force a later shot or even get a touch on the shot, but it's still unlikely.
Bonucci's strengths are not in this area, and being forced to play as a covering defender hangs him out to dry. He was fine with 'bodyguards' Barzagli and Chiellini. He just about gets away with it having an elite young defender like De Ligt covering, but you can't expect him to be the defensive leader.
But don't take away from Sassuolo that it was a perfect pass and first touch, they did everything right. Demiral was actually very close to Bonucci, which gave him a chance to intercept (Demiral is a natural defender who wants to protect the goal and his partner), but it was threaded perfectly, and the touch opened himself up for the shot.