Columbia Encyclopedia World Factbook Columbia Gazetteer American Heritage Coll. An Introduction to the Study of Speech. Page 201 most languages would present such irregularities of morphological contour as to lose touch with their formal ground-plan.
Sound changes work mechanically.
The dative singular fet, however, though justified historically, was soon felt to be an intrusive feature. Fet as a dative becomes obsolete. The singular now had o throughout. But this very fact made the genitive and dative o- forms of the plural seem out of place. The nominative and accusative fet was naturally far more frequently in use than were the corresponding form of the genitive and dative.