Lack of originality or a stepping stone?

I need to try and understand something. Every time I search for something to read on here, everything I find has to do with bands. Why is that? Is it a lack of creativity? Or is it just a stepping stone for authors to build on? I don’t like reading stories that have been taken from other people’s work—Harry Potter, Fall Out Boys, Twilight.

If the story is taken from a book, I have the expectation of the story being written in the same style. If it’s taken from a movie, I expect the same personalities to stay in play. And being taken from an actual band? I just can’t get into stories like that. Multiple users use the same person but with different personalities for that said person and it just becomes too confusing for me.

These are not rhetorical questions. I would very much like to know: Why do you not use your own entire assemblage of original characters? Why do you play off of other work? Is it to help you progress as a writer? Or is it just a wishful fan thing?