This is exactly it. Mundanes see anything beyond their football games as "weird shit" and science fiction has become the catch-all term for that weird shit. And, as insecurity has grown in genre fandom, the trend has been to go along with those low standards in desperate hope of acceptance. It's like the nerdy kid in junior high school who laughs too loud at the jock's stupid jokes-- it's awkward and embarrassing..
I think that's a stretch. You could just as easily argue that some fans are still so traumatized by high school that they persist in seeing the "mundanes" and "the masses" as the enemy--and are ever intent on finding new ways to prove that they understand what science fiction is all about better than the jocks and cool kids. 'Cause god forbid we let those
people into our exclusive, little fannish club. They might actually confuse robots with golems!
Better to keep pointing out what "higher" standards we have than those silly people who don't insist on our rarefied, ivory-tower definitions.
It's funny. Once in a blue moon, I stumble onto a bookstore that tries to keep the sf and fantasy books separate. It's always a mess, with the same authors (and sometimes even the same series) scattered across the store. Where do you shelve Gene Wolfe or Ursula K. Le Guin or Piers Anthony or Marion Zimmer Bradley or Andre Norton or Orson Scott Card or Poul Anderson or Ray Bradbury or whomever? And do we trust some poor clerk to figure out whether "Witch World" is fantasy or science fiction? What about "The Shadow of the Torturer" or "The Anubis Gates" or "Dragon Riders of Pern"?
Honestly, it's easier just to put them all in the "Science Fiction" section.