Answer by Amar Prabhu:
The reason is because they are highly intelligent creatures. Having observed monkey behavior (the Indian rhesus to be particular) plenty of times in this regard, there is a simple explanation. Consider the cavendish banana:
The stem (the part where it is attached to the rest of the cluster) is the toughest part of the banana. Pinching the stem to get to the fruit is much more difficult than getting to it from the bottom. The monkey will choose the path of least resistance almost every single time if the banana is ripe. Monkeys deserve respect and admiration in this regard as I was surprised and taken aback because most people, myself included did not know this.