He's boring.
He can practically do anything outside of resisting kryopnite.
Who wants to watch a movie where the character doesn't have to overcome and struggle past something?
No real conflict.
this isn't true....supes isn't boring and there is plenty of 'real' conflict in his stories from him as a character, to how he's trying to relate to humans, to his villains, to how the world reacts to him, etc...