He didn't. The developer did. He was overwritten. The act of pulling the developer inside the game was his last resort of saving the heavenly realm from being destroyed. If anything he's a real king and true ruler with great decisions. He didn't hand his powers out easily to the MC, he thought everything so well that he was counting on the fact the developer knew the game so well and he'll understand the messages behind the missions he gave the MC
Agree agree!
And King is so smart to put MC soul into his body and hide his ownself/soul somewhere no one knows.
And the reason was if he stay, he will be bound by the pact (which the MC put into the story on a whim) and cannot defy the enemy leader's word.
He don't want to become the puppet of his evil sister and ruin the world with his own hands.
But why doesn't jaeseokcheon know he created that crappy universe ┑(￣Д ￣)┍