it's fear, more than anything. Imagine if Dio yelled ROADO ROLLA DA but instead of it hitting the thing slipped out his hands and broke his leg. He thought he had the invincible ability, but there was something that directly manipulated you, with time frozen
Ahhh. I was seriously annoyed as to why he was going so far to try to kill a "useless skill." Its because of his pride. Classic. Though to be fair time manipulation is seriously broken.