The short answer is, I don't know, but here's some speculation...
First off, what variety of banana is it? If it is a seeded (ornamental) variety, lack of pollination could explain the aborted fruit.
If it is an edible variety, I don't see an obvious cause of the aborting of the fruit. It appears the rest of the plant is healthy, including the rachis (the stalk the fruit are attached to). That suggests that there isn't some disease or nutritional problem that is affecting the entire plant and the problem is confined to the fruit. It is possible that there was some major stress (e.g., lack of water or very hot, dry conditions) at a key point in fruit development.
If it isn't a seeded variety, then just ensuring optimal growth conditions is your best bet: heavily mulch to retain water and deliver some nutrients, fertilize regularly with something high in potassium, water adequately, etc. Also, make sure micronutrients like boron and calcium are at adequate levels.