I think its because to see all the endings you have to fight lavos over a dozen times and you dont have to play through the whole game to get to him as he is accessable at any time so the build up is sorta disregarded as you'd normally have to play through a whole game to get to the final boss. After owning this guy for the fifth time he begins to become far less threatening and becomes more of an annoyance. Not to mention you dont have to worry about burning up all your mega elixers when you fight him which makes the battle even less fear inducing.