Editors aren't interchangeable drones, like bottle cap washers in a beer factory. Each editor has his own interests, skills, schedules. So some categories might get very carefully tended, simply because a lot of active editors are interested in them. Other categories might get less activity simply because there aren't enough public-spirited surfers interested in the subject. So we might have enough editors to review all Gift Shops on the day they were submitted -- and yet decide there was something far better for them to do.
And even if the concept of "enough editors" could be extrapolated across the directory, it would still be meaningless. "Enough editors for WHAT?" to meet the demand? But nobody has a right to demand editors! To provide the information surfers want? But if surfers want that information badly enough, they'll find it, and if they want it published badly enough, they'll help publish it. If no surfers really want it that badly, then obviously the ODP has had enough done to satisfy everyone well enough.
We have enough editors to do what the editors think is worth doing most. We have enough editors to do more than any other general-purpose website review system has ever contemplated doing. But we don't have as many editors as we'd like. We don't have enough editors to make sure all the things I'd like done get done without my help. We have ... the editors we have, and we try to make the best of them, which is the only way to attract more editors.