One reason is that different shapes of pasta complement different kinds of sauces and recipes.
Can you imagine making macaroni and cheese with angel hair pasta? It would turn out to be a sticky unpalatable mess.
On the other hand, a light olive oil and herb sauce would be lost on lasagna noodles.
Those twirly noodles can hold on to a medium weight marinara, and are also good in a pasta salad.
It may also be that some Italian women had too much time on their hands. :)