By now, I'm sure everyone has seen/heard the over the top love fest and claims of him being "this generation's Jordan" (apparently Jordan was the fourth best player of his generation).
Some of it is lip service. James, for example, has clearly never been his biggest fan, but as a longtime face of the league, he tows the company line. Much of it, of course, is genuine, because Bryant is their ideal image of what a basketball player should be. From the dark skin, to the profuse sweating, to the constant scowling, to the berating of just about everyone at one time or another, to the arrogance, to the trash talking, to the posing, to his size, position and the style in which he plays. The selfish, iso balling, high degree of difficulty shots, etc. He's everything they think of when they think of basketball.
Duncan is, of course, the polar opposite in virtually every respect, so of course many of them don't hold him in the same regard. The vast majority also know nothing about and in many cases shun advanced stats, which doesn't help his cause.
This is precisely why the vast majority of NBA players, particularly former ones, shouldn't be in positions of power in the league, have a hand in voting for anything involving the league or have their opinions taken seriously. Time and time again, they prove that they're nothing more than genetic lottery winners, who know little about and have a distorted view of the game.