Why? Curly/hollow pasta holds more sauce than flat does. OTOH, flat pasta can be stored much more compactly. (As one of the commenters notes, small is not necessarily beautiful when you need to catch the customer's eye at the grocery store.) So if you need to store a lot of pasta but don't want to lose the curly-factor, it would be nice if the pasta curled up when you cook it.
They tried stamping ridges on one side of sheets of flat-rolled pasta.