The reason is:
Rose:
24.7ppg, 4.3rpg, 7.9apg, 1.1spg, 3.5to
44% FG, 34% 3p, 85% FT
Westbrook:
22.1ppg, 4.6rpg, 8.4apg, 1.8spg, 3.9to
44% FG, 33% 3p, 84% FT
He's a point guard in the rose mold, who happens to be the leading MVP candidate.
CP3 is the best in my mind - super efficient, takes care of the ball, distributes well, and plays good D.