I still sometimes see people say things like “Oh, but that’s just a crime show, so of course it doesn’t have a big fandom”, as though fanfic-writing geekiness is somehow inextricably tied to sff geekiness. I have gotten the Fake Geek Girl thing from dudes at geek meetups who like Game of Thrones (possibly the most mainstream taste known to mankind) but think that writing fic for old cop shows nobody cares about anymore is “mainstream, not geeky”.
But when Starsky & Hutch became the new hot thing with fanfic writers, “Media Fandom”, which had meant “Star Trek fandom” (as opposed to sff book fandom) started to be something other than just sff, and the pattern holds true today.