Pac already does try to move to the right in order to step side-wards and open up the angle for his left hand, it's just that Marquez can ready his feints and pivot in-range so that he gets superior positioning by the time he advances. Manny being the aggressor and initiating gives JMM the split second needed to anticipate and turn, subsequently timing him. He offered much less lateral movement in the fourth fight, and combined with Manny's emphasis on feinting, Manny was able to attack from both sides at certain points (outside the lead foot towards JMM's left, or all the way outside towards the right). JMM was waiting for the right opportunities to land hard, and he took advantage once they came.
If Manny ever purposely turns towards JMM's right, it's usually to make space in the ring to then turn back the other way while throwing. Martinez does this a lot.
I'd never go so far as to say one fighter could never beat another, but it doesn't look likely that Manny ever outboxes him or outfights him.