I don't really agree. I remember getting books from the library in the early 90s that talked about UFO conspiracy theories. There was a lot of weird stuff on TV, before the X-files, like In Search Of (which I think was from the 70s).

Arthur C. Clarke's Mysterious World was a thing among such things. It was present in popular culture, it wasn't obscure, but it did culminate with X-files for sure.