Simple answer, money. If the money is right somewhere else then they could take it. However, Ibaka and Harden's stocks have plummeted after these finals. Hopefully they both can come back stronger, they're both one of the best at their respective positions and other teams would pay good money for them. I hope their family attitude stays with them and they stay with the team. I don't think they'd ditch a good system and chemistry with the team for money though, they seem to put their values higher than a dollar sign

