I think he doesnt trust him either to start/work/combine in the way he likes, but in this formation IMO its strictly task wise. Morata even if losses possesion too much and is bit awkward wide, is atleast little used to that position in terms of what Allegri asks for specifically and how he uses that space (I seen him play it for Real too). While Dybala cant really play LW and is more suited centrally and with freedom to roam.
But mainly IMO its about Allegri not trusting Dybala yet to do the task. Which is harsh if so. But he is the one tasked to make sure we win.