When trying to give your banana bread a tender crumb, there are two important things to take into consideration. The first is that you need to add enough fat to the batter. In this recipe, the fat comes from the eggs, yogurt, and butter, but if you decide to substitute out these ingredients be sure to substitute them for other forms of fat (such as coconut oil).  The second thing is that you need to be careful not to overmix the batter.  Once the wet ingredients are in, the gluten in the flour will start to form long chains, which is exacerbated by mixing the batter. Overworked batter will make a tough and chewy loaf of banana bread. This is why it's important to make each stroke of your paddle count as you fold the ingredients together.