Ditto, all of the OZ books and many other, successful fantasy and SF books!
The best Sci-Fi (in my not-so-humble-opinion) deals with matters of physics, consciousness and the links between the mind and space-time (which was a huge part of Dune.)
It’s tough to see how that stuff would translate onto the screen. And even tougher to see how you could sell the result to audiences raised on constant gunfire and an explosion every 45 seconds, dutifully interspersed with gratuitous obscenities.