In one of his least informative articles, (“Where Do the Virtues Go?”, 2004), Michael Dummett attempted to explain why the three Moral Virtues, (Justice, Fortitude, and Temperance), are the most variable Tarot trump subjects in their placement. He offered a hunch. He then pondered whether an odd document from 1457 might corroborate that hunch. After he determined that it did not actually support his guess, he concluded by saying that he still liked the idea. “The hypothesis remains plausible.... What other hypothesis will explain the strange fact of the varying positions of the Virtues in the trump order?” The question is misguided, however. There are over a dozen different orderings, and about half the trumps change position from one ordering to another. The primary question is why each locale in 15th-century Italy insisted on moving the trumps around a bit. The secondary question is why they kept such re-positioning within the three groups which Dummett identifies in his first paragraph.
In answer to the first question raised at the top of this post, the trumps were re-positioned in each locale because of what I have termed the “civic pride” motive. Tarot was a very popular game, and each city wanted its own deck/trump ordering. They changed the sequence of the trumps and altered the iconography a bit. This way the local deck and game (trump order is one of the most important rules of the game) was recognizably theirs. (As an aside, trump ranking is also the thing which ties the allegorical hierarchy to the game itself.)
The answer to the second question, why they kept the three groupings intact, (and why the changes in iconography were mainly minor), is that they wanted the game to remain Tarot. Subjects within each group are of the same general type, whether representatives of Mankind, conventional allegory, or eschatological events. Trump subjects could be moved within each group, and the pictures altered a bit, without changing the overall story of the trumps too greatly. That way the local deck pattern was very similar to everyone else's and yet distinctive enough to be immediately identifiable.
This civic-pride hypothesis is corroborated by the fact that almost every known deck or documentation from different 15th and 16th-century Italy has its own design: Slightly different ordering and slightly different images. This is in striking contrast to the usual manner in which playing cards migrate from one place to another, keeping the deck the same. Outside of Italy, for example, virtually all decks followed the same ordering as long as the standard trump subjects were used. Only in the world of Italian city-states during the Renaissance was this civic pride motive active.