Female servants were in charge of buttoning their mistress's gowns (since the buttons were usually in the back). They tired of attempting to deal with buttons that were, from their point of view, backwards and, as such they started reversing the placement when making or repairing them. Another possible reason is so that men can easily undo blouses as, from the front, buttons are on the same side as a man's shirt. One other theory is that women were normally dressed by their maids, while men dressed themselves. As such, women's blouses were designed so it could be easily buttoned by the maid but that of men were designed so it could be easily buttoned by the person wearing it.