“Check out this Wicker Man-looking place!” Morty exclaims. So he knows 1973’s Wicker Man—but not Iceman or Encino Man?
Knowing one old movie doesn't mean you know all of them...
And like someone pointed out on that site's comments, Nic Cage did a remake semi recently. I don't know about the 70s version. But I knew it was a terrible Nic Cage movie.