Why does leftover pizza dough make terrible bread?
I'd say your problem is that the yeast has exhausted the food in the dough before you even get the leftover dough in the fridge. When you pull it out the next morning, the yeast does nothing or very little because there are no more sugars left for it to eat. And not only will this prevent rising, it will also limit browning because it's at least partly the sugars that brown in the oven.

You could work some more flour (and water, to maintain hydration) into your dough as yeast food--maybe even a little sugar if you want--and then rise/form/rise and bake. But at that point you're doing what @tmow suggests--just using your pizza dough as a starter for new bread.