Quick breads should be moist but not soggy, so we often need to get rid of extra liquid in the batter. In some recipes, like zucchini bread, we squeeze all the excess water out of the shredded zucchini to avoid a soggy loaf. We can’t squeeze our pumpkin puree (that would be messy!), but cooking has the same effect.
With heat, some of the water in the puree evaporates, helping keep the finished loaf moist but not soggy. As a bonus, cooking the puree takes away the raw pumpkin flavor and gives it some earthy caramel flavor. Add a little cinnamon and nutmeg, and this bread smells (and tastes) like autumn.