That's the question that Business Insider asks and tries to answer:
We're tempted to predict the imminent bursting of the bloated cupcake bubble. Surely some of these shops will be out of business within the next couple of years. But cupcakes may be more than a passing trend. You see, cupcake sales profit from a deeply anti-social tendency in America. While normal size cakes are made to be shared, cupcakes can be eaten alone. They are the dessert version of the "Bowling Alone" phenomenon. Even when shared with friends, cupcakes are less socially taxing than ordinary cakes. A full sized cake must be cut up and placed on plates, served individually. With cupcakes, you just plop down a tray and walk away.