The starfighters fought like spacecraft 'cuz he had the special-effects people copy the scenes from old WWII movies.
Sheesh.
ANYWAY, not to get off-topic or anything…
I don’t think that’s entirely it. The problem doesn’t arise simply from a movie being an adaptation from a book, but the fact that if you were to make a movie using the novel as a script, you’d wind up with a movie that’s seven or eight hours long. So SOMEthing has to go, and usually it’s something critical. Hence, the difficulty of making a good book adaptation.