He doesn't want the Demon Lord dead, he wants the MC to keep him alive, most likely long enough for the douchebag creator to get back whatever the Demon Lord stole in the first place.WTF.
"Look, you didn't fuck the girls and you made it a paradise anyway. So we're redoing this shit so you kill the demon lord… who had been long dead before you even got to this world you're going to go kill him again to get this world on track."