His goal is to win the fight. As all fighters goals are.
He just uses the tools at his disposal. If he had the power of Rumble I am sure he would not hesitate to go for one shot knockouts. As it is his strengths are IQ, conditioning, timing, and positional dominance. Against lesser opponents like early in his career he could still finish fights no problem. Against Diaz, Shields, Fitch, he is forced to play the long game.
Same reason fighters like Barboza and Lando looks unstoppable head kicking scrubs, but fold like lawn chairs against tenacious fighters like Tony and Khabib. Same reason an otherwise consummate knockout artist like Conor ends up point fighting Nate in the rematch when he realizes he can't just blitz and put him away.