TOS Khan was prepared to sacrifice his and Kirk's crew just to prove he was superior to Kirk.
I got the impression in TOS that his crew was a bunch of arrogant supermen and superwomen like himself who were united under his rule that he respected but needed to dominate.
Perhaps after his hardships on that planet he grew to 'love' his people in TWOK. Of course revenge was a higher priority than their lives.
Maybe nuKhan grew to love his people or realised he was alone without them in nuTrek. Marcus had a year to play mindtricks on Khan.