The only reason OKC wouldn't do this is because Westbrook's potential is sky high, he's young and they could get more years out of Westbrook down the road. CP3 is one of the best point guard's in the NBA, but he'll be 30 in about 4 years while Westbrook is still 22 I think. They probably just think Westbrook is going through some growing pains and needs more time to develop. Like he's already an all-star at his age.
I dunno, I'm searching for reasons why it isn't happening.