@farmerman,
I think the why is somewhat about texture and form, as Beth says (fusilli and such come to mind), and some is down to regional and temporal variations. A single simple dish can vary from village to village, with strong proponents from each place. A certain shape (strozzipreti, for example) could have been - I conjecture - started by one mamma or indeed, one nun, centuries ago. I dunno, I haven't read the book yet, and it is billed as a food history.
An interesting book I read several years ago by Mary Taylor Simeti was about Persephone's Island, Sicily. That got into pastries for different feasts and some of the background for that, if I remember right.