He doesn't like seeing King Popo and Queen Maria laughing, having fun, or being happy.
And WHAT happens when he sees the King and Queen back together?
"He didn't like it ONE BIT!" (Indeed!)
So to put an end to the King and Queen being together…
"I'll make sure your apart FOREVER!"
on King Popo and Queen Maria,
turning them into mountains!
King Popo and Queen Maria CANNOT move, they COULDN'T speak, and they CANNOT say, "Te amo".
And he just leaves them there.