Maybe you don't find superhumans that appealing? I know a guy that can't understand why I don't want to watch movies about regular people instead.
It's cliche'd as hell but the movies are about hope, strength, determination. All that BS done by someone way more powerful that ourselves (usually). Like 99% of hero stuff is a metaphor which boils down to: even the strongest, toughest, smartest, quickest people have their own tests and their own demons. Nobodys perfect.
Obviously individually there are loads of other things that the various sub-genres of superheros are about and going further than that, each individual superhero is about.