The problem is Bonucci has no idea how many Genoa players are in the box. You can watch the clip and tell me if Bonucci even looks once over his shoulder. He's literally marking him and then just steps away. If it's Scamacca by himself, then Alex Sandro can stay right on him and Bonucci can cover the zone in front.
But Alex Sandro has his own man to mark, so Bonucci should put his big boy pants on and mark the number nine that I'm sure Pirlo wants marked at all costs.
You can even see AS's reaction after, absolute disgust at Bonucci. And he's probably our quietest player.