It's the disease of more and the Cavs momentarily prevented the Warriors from succumbing to it with our 2016 championship.
If a team wins for long enough eventually everybody wants more. These guys are competitive, and once it's obvious their competition isn't with the rest of the league, they start looking at their teammates. They'll start wanting more touches, more shots, and more money than the guys around them.
If the Warriors win in '16, who knows? Maybe Klay eventually wants to go lead his own team and be "the guy". If KD doesn't go and the Cavs end up with championships in '16 and '17, I'll bet Kyrie still goes out on his own looking to be the alpha.