I have an unfinished blog on this subject, it's been sitting for a long time, it includes the images already posted upthread, but I'm beginning to realize I'll never have time to finish it, so here is a very very condensed version of what I think is happening in these drawings...
Throughout the Middle Ages, there were schematic attempts to tie everything into one neat system that could be illustrated in the popular 4-8-12 diagrams. R. Lull was one of the important catalysts in representing information in a schematic way (often as trees or rota) and his ideas spread quite rapidly to manuscript diagrams. Liber Floridus is a good example of wrapping up related ideas (as they saw it) in neat round packages.
At first, the drawings of "the elements" or "the humors" didn't usually include humans, but textual charts or personification of "the
humors temperaments" were becoming more common in manuscripts... these were sometimes a single person surrounded by four divisions into humors, or a row of people or a 2 x 2 block...
As can be seen, some illustrators got the idea to represent them the same way as elements, in a rotum, with heads pointing outward.
Those who were representing gravity also caught on to this idea and you start to see drawings of four humans standing at four points on the earth with a "hole" in the center into which a rock falls. Different concept with a similar visual presentation (in fact, often you have to glance at the text to know if it's a "gravity" picture or a "humors" picture). Houghton 101 also has some of the early schematic rota.
Perpetual calendars and wind diagrams were adapted in this way, as well. In fact, wind diagrams have one of the longer histories of rotum representation, and may have inspired the development of some of the "elements" diagrams into rota as well. Even urine bottle diagrams were eventually organized this way.
So, to get back to the diagrams posted upthread... two of the more common ideas represented as rotum were the elements and the
humors temperaments ("
humors temperaments" rotum below can seen in Huntington EL 26 A3).:
So... it seems to have been a fairly natural evolution in terms of the philosophy of "all things being related" and fitting into neat little Galenic boxes that some illustrations would be designed to consolidate concepts like "elements" and "humors" and " temperaments" into one diagram OR some of the illustrative figures from one might be borrowed to illustrate the other, since the two concepts were often within a page or two of each other in manuscripts.