A few of us in Dalayan Beginners were just discussing the lore aspect of this the other day. From an in-universe perspective, think along the lines of donfolstar3's post, but from a strictly practical standpoint, it all comes down to client limitations. Frogloks were enabled for Necromancer, Rogue, and Shadowknight as of the 08/11/05 patch on Live, and our client is technically from just prior to that period. (Yes, the Titanium install was always recommended for SoD, but to the best of my understanding, our specific client is actually pre-Titanium!) Incidentally, this limitation falls in line pretty well with the Taldorians' affinity for Malath.
Unless Waldoff & Co. deliberately break these options at character creation like they did for the Berserker class, it is possible that Frogloks will indeed be enabled for these three classes with the advent of 3.0. Seems the jury is still out on this, though!