The Eye of Agamotto Changes Hands

They were said to be Parallel Universes, but since they were Parallel Universes, there would naturally be major differences. Stephen Strange believed that He-El's existence, as well as his dreams of living the life of another version of himself in a Parallel Universe, were significant differences. The things of this world ought to be different, yet still arrive at the same destination by different paths. That universe had a Thanos who wanted to wipe out half the life in the universe.