There are many theories for why the Tuscans started making their bread this way. The most likely is that salt was heavily taxed during the Middle Ages, and so the bakers in Tuscany started going without. Even after the tax was lifted, the bread tradition stayed.
Salt-less Tuscan bread is really not intended for eating on its own. It’s usually served along with the main meal and is meant for sopping up thick, rich sauces. The bread doesn’t compete with the flavors in the dish, and both are enhanced.
If you’d like to try making Tuscan bread at home, there are good recipes in The Bread Baker’s Apprentice by Peter Reinhart and in Local Breads by Daniel Leader. It can be fun to make one loaf without the salt and one loaf with, just to see how different they turn out!
Have you ever had Tuscan bread?