Its kind of fucked either way. They’re too short but a lot happens because each book is broken into thirds that are separated by huge time gaps, and inside those thirds there are also time gaps. A movie, even a long one, would be incredibly disjointed and the pacing would feel bizarre.

I imagine it’s probably why nobody has made it a series or movie before even though it’s such a beloved sci Fi series. You’d have to take a lot of creative liberties with it, which is for better or worse, what they’re doing.