The most common reasons are over mixing which can cause the gluten in the flour to develop too much, resulting in a dense texture. Also using bananas that are not ripe enough can cause the bread to be dense and not sweet enough. Other reasons include using too much flour: If too much flour is used, it can cause the bread to be dense and dry. Not using enough baking powder or baking soda can result in a dense texture. Finally, overbaking the bread can cause it to become dry and dense.