I've been racking my brains trying to think of any RPGs that don't have some form of magic or fantastical technologies that might as well be magic. Twilight 2000 and Delta Force: America Strikes Back! are the most mundane settings I can think of as as there's no magic or super science in either of them. I still think part of Shadowrun's success compared to Cyberpunk are due to some of the factors I mentioned, but at the end of the day I think you're right. A mundane hi-tech world just isn't as broadly appealing as fantasy. There's something about fantasy that makes it easy for people to dive into.