What's the deal with the Rocky Horror Picture Show?

A movie theater near where I live has been showing this movie twice a month at least for the last forty years or so. And there's all kinds of audience participation, apparently, including people like acting the movie out onstage. And this is going on all over the world? What is so interesting about a movie that's almost fifty years old?

Whats the deal with the Rocky Horror Picture Show?
What's the deal with the Rocky Horror Picture Show?
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