Kobe's demise as a shooter and inability to become a better teammate
Kobe would get assists, but never seemed to really facilitate in the way Lebron does. I thought there was a moment of transition a few years ago when he averaged a career high in assists, but it was always about him eating first, as he never really shot less, the ball was just in his hands more than ever. Lebron gets enjoyment out of facilitating, you don't see that with Kobe.
The odd thing is that he's a damn good facilitator when he wants to be. He could have extended his career a few years had he made the shift, but the guy is just so stubborn he'd rather retire than give up shots.