How come when Zordon was destroyed, some of the evil still existed?
Well, the real reason is that Power Rangers would be pretty boring if there weren’t any villains. But I know that’s not what you want to hear. My personal theory is that Zordon only destroyed the monsters, creatures, robots, and whatnot directly involved in the final invasion — those with close links to Dark Specter. Dark Specter was the ruling force of evil, and Zordon was his opposite — the ruling force of good. And, like matter colliding with antimatter, when the “Z-Wave” was released, it destroyed Dark Specter’s legacy. Plus, if you want to get metaphysical, “evil” isn’t really something that can be destroyed without destroying free will, and destroying free will would be an evil act in itself. Zordon didn’t truly destroy evil. He merely destroyed an enemy army.