Probably because CP3 is a PG.
Point guards are not relied upon to carry the team, especially pass first guards. They need players around them to compete at a higher level. Cp3 is a pass first guard who would rather pass than shoot. He can close out games because he's extremely clutch, but he doesn't have the extreme pressure other stars have. Melo on the other hand, is seen as the go to guy to score and carry his squad because of his position.For all the points he scores, he can't get his team to win when it counts that's probably why. Ain't nobody on Deron's head for not winning a championship. But people will be on Durant in a few years. When your asked to score, your asked to carry your squad to.
That's why the position is overrated and those who build around them are retarded