Well, you know...it was the classic problem all over again. I mean, they just couldn't call them Entwives, could they? And Treantwives is awkward to pronounce. And since there were enough comments about slutty-looking fey in the MM1, they probably went with the path of least resistance...you can call this dryad a lot, but slutty it ain't.
Frankly, a monster the players can stab is more useful to me than a monster they can't. This looks a lot more stabbable than the "hot chick with nonviolent powers" dryad type.
there's a joke there... but I'm not going to be the first...
Me, I prefer the "hot chick with nonviolent powers" dryad. D&D is NOT solely about combat. Having a fey that charms her opponents, occasionally keeping the ones she fancies, is infinitely more interesting than that topiary abomination.