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.

I own a pizza restaurant and I always use my left over pizza dough the next day for making bread. Rolls just don't work. Take your dough and roll it into a loaf, thoroughly coat with olive oil or veg oil. Let rise for a couple of hours. I usually do 2 to 3 hrs because it is cold. I then bake till nice and brown, varies in the restaurant, because sometimes I throw it in a 550 down to a 350 degree oven. Depends on what ovens are empty at the time. My customers LOVE this bread. Good Luck.

Because of the digestion process of the yeast. If you use biological yeast, you can use this fermented dough as yeast to prepare other pizza or bread.

Some families in Italy (it was our case till some years ago) use the same piece of fermented dough to prepare pizza and bread every week.

EDIT

Yeast fermentation is better achieved when the temperature is around 75 F and 85 F (23 C and 30 C), as you kept the dough in the refrigerator, you probably need to keep the dough in a warmed place so that the yeast is reactivated, you can add a bit of flour and water, knead the dough at least five minutes (and add flour and water if it's needed).

When you are finished leave the dough in a warmed place.

If it still doesn't work maybe your yeast is exhausted (R.I.P.).

If you want to have more information about fermentation I kindly advise you to read to take a look at this article.

When I think "bun", I think of a soft, possibly buttery roll. It typically uses a softer flour, you cut in butter to get in flakiness, and you might have eggs, milk or sugar in it to promote browning before the middle's gotten too firm.

If I were going to try to use the dough, I'd go for a similar style of bread to the pizza crust -- focaccia, rather than try to make it something it's not. (focaccia typically has oil in the dough, where pizza crust doesn't always, but it should still come out okay as a flatbread)

You might be able to pull off a more rustic "country loaf" type of bread with the dough, but I don't do enough baking to be able to compare what pizza doughs are most similar to. (baking's one of those things that I still refer to recipes every time, I don't have 'em memorized)

I agree with others - you may get a decent roll out of the dough, but it's not going to be super soft/flaky/buttery like a bun. While it's not always the case, pizza dough usually is made from bread flour, which has more gluten than all purpose white flour. This will make the dough much more chewy.

However, I have a tip for making the dough rise after it's been in the fridge...

A great way to accomplish the moist heat that you need in order to reactivate the yeast, boil a pot of water - doesn't have to be very large, perhaps 2-4 cups worth. After it comes to a boil, place the pot on the lowest rack in your oven, and place your dough on a pan on the top rack. Close the oven door and check back every 5-10 minutes to see how its doing.

This should make the dough rise much better than leaving it out at room temperature. However, if you don't get much lift at this point, your yeast probably have consumed the sugars.

As I see it, the recipe you link to differs from the typical whole wheat bread recipe in 2 significant ways:

1) There is no oil or butter in your pizza dough recipe. 2) 1/2 tsp of salt is rather little for 2 cups of flour. Try a teaspoon, or maybe 3/4 tsp to begin with.

Certainly people add butter to make bread more delicious. A pizza covered with melted cheese gets even more of this effect of added fat. And pizza toppings, including the sauce and cheese, are often rather salty. So you may not want to add salt and fat to your pizza dough, even if that helps the bread. What you could do is make rolls with the leftover dough, and before baking brush them with olive oil, and sprinkle on some salt and, optionally, thyme and/or other green herbs.

Usually, pizza dough has a high oil content, where bread dough does not. This is a big difference in texture. The pizza dough is more dense than bread dough so it does not rise nicely like bread does...therefore the bread or rolls made from pizza dough are more dense, tougher, and not what you want in a regular type bread or roll.

What is happening to old pizza dough is that the yeast gets exhausted, as several other answers mentioned. But the big advantage of your dough is that it 1) has developed nice tastes through prolonged fermentation, and 2) has unbelievably good gluten formation. More than once, I have left a 85% hydrated AP-flour dough in the fridge for three days. At mixing time, this is barely kneadable even with ice-cold water and some acid. But on the third day of retardation, it behaves great - assumes a round shape on working, does not stick to fingers, etc.

This dough will not rise any more if you just form it and bake it. But you have just invested the time in creating the best pate fermente, so don't waste it. Instead, mix the ingredients for half a batch of the same recipe, and add an equal amount of old dough, warmed to room temperature and cut in small pieces. Knead everything together and treat as normal lean bread dough (first rise, degas, second rise, etc.)

There are two prerequisites here, and one limitation. First prerequisite: your dough was not overyeasted from the beginning. Some quick-rise recipes will use up to 10% fresh yeast. These will produce stinky byproducts during a long retardation. Second prerequisite: you retard your leftover dough (put it in the fridge) as early as possible, the best time is right after mixing. And the limitation: this works best when the new dough is the same type as the old dough, so you will get a lean-ish continental bread out of the new batch (I suppose that this is what you are using for your pizza). I wouldn't try making sandwich bread with old dough.