I'm guessing in Conte's mind Pogba covers Vidal's (and to some extent Pirlo's) role in his tactics but not Claudio. Just see how many times Claudio got subbed off with Pogba, and compare the same thing with Vidal/Pirlo being subbed off with him.
Conte's a midfielder FFS, he knows what he wants from his midfielder, he knows the game. Now this is pure speculation but 4-3-3 didn't really leave us here, Claudio was supposedly to take the role as the third (hidden) forward with his run.