Why Does Taco Bell’s Mexican Pizza Keep Disappearing?

You probably know exactly when and where you first fell in love with Taco Bell’s Mexican Pizza - a marvel of fast-food engineering so beloved that it's almost a cultural icon. But how did this crispy, cheesy, tomato-y masterpiece come to be? Why did it disappear? And is it back for good, or is it just back long enough to make us fall in love again before breaking out hearts like a store bought taco shell?