To be fair it's possible he has worked on some other things in the meantime but just hasn't said anything about it (after all, the WormFork Book took us all by surprise because we had no idea he'd even been writing it until he announced the release date).

...but with that said, I'm just as unimpressed as you are that this is apparently the best he could manage after ten years and multiple drafts. Seriously, dude? That's it? Really?