Why did Gunn feel the need to change Jor and Lara from being concerned parents who send their only son away to build a better legacy than that of Krypton to world conquering warlords? Why did he make Jor-El into Zod?

I know Snyder laid it on too thick with the savior stuff but this feels like too hard of a change. Donner and Brando's take is still best.