I am just going from memory here...I believe Westphal's contract was soon to be up for renewal and Paul and Red were far, far apart in prelim $ discussions, so Red basically traded Paul for a player he had always liked - Mr Scott. I think there are other cases where sides were far apart, Red lost patience, had the power and made a trade.
With Cedric for Bill Walton, it was also a money issue and Red was really frustrated with Maxwell's casual approach to rehab.