The fact that you had no idea where the hell that monster came from!
Nowadays, Hollywood needs to explore every nook and cranny that their favourite stories have. So we need to see in all the gory details how Darth Vader actually used to be an annoying punk like Anakin Skywalker and was then turned into the menacing machine called Darth Vader. How Batman became Batman. How basically every interesting super hero, villain, or otherwise interesting character became what they are.
Who the hell wants to think about how their girl-friend or boy-friend pooped on themselves in their diapers when they were toddlers? Stories and characters are interesting or sexy because of the things we don’t know about them.
That is why origin stories suck.