to me i just think that sasuke is just hunngry for more power ever since he met his brother again, and after witnessing the unlimited power of narutos kyubi chakra
so thus he just go greedy and now hes just searching for more power so that he doens feel weak still i think he d just a selfish bastard who shouldnt have been put int the story anime in the first place but hey hes int eh anime so cant stop them now