I suspect one of the difficulties with getting a really good novel into script form is capturing the internal dialogue of the characters in an intelligent way without resorting to a “wonder years” narration gimmick.

Orson Scott Card’s Ender series, Heinleins Stranger in a Strange Land, Asimovs Foundation series… all of them rely pretty heavily on exploring the thoughts and feelings of their characters.

It may be why short stories are often better vehicles for Sci Fi than novels.