Even if that's the intended meaning of literally, it is still a reckless exaggeration. I'm pretty sure that Stephenson's endings are no more abrupt than some of Shakespeare's (check out Hamlet and Macbeth) or some of Frank Herbert's (see Dune and Children of Dune), and I never hear anyone go out of their way to describe either of them as being unable to write endings.
> some of Frank Herbert's (see Dune and Children of Dune),
I mean, Dune does in fact end mid-story, which is probably worse.
Everything from Stephenson after Anathem is an unremitting slog. He needs an editor who won't back down from telling him he needs to cut a third of his pages.