>>212935979
Zod literally says before the last battle that he doesn't have anything to fight for anymore.
No more chances to restore Krypton so he has no purpose other than to fuck up everything Superman cares for.
Also he was a high skilled trained General by birth that was getting used to Earth atmosphere, getting stronger. No more phantom zone to throw him into.
He was one of the most powerful beings going rogue, how the fuck would you stop something like that?