Because they are human and people occasionally make mistakes.
Occasionally? Nearly every article they've released has rules issues in it. Issues that we catch within 5 minutes of the article being released. They've done the same but do have a better track record with the FAQ's.
The fact that they're human doesn't mean anything. Proper editing takes the human factor out of it, by having several people who ideally understand the subject read it and fix mistakes before the final release.
There is qutie frankly no excuse for the issue with the large ship MoV rules. First off they fixed something that was IMO at least not broken, and then in fact broke it. Something which we spotted almost instantly.