'Cupcake' instead of fairy cake or bun

I find this one hard to understand - when I was little, they were always 'buns', 'butterfly buns' if the top was cut in two to make wings with a blob of buttercream underneath, or possibly 'fairy cakes' if they were fully iced.
Fairy cake is so much nicer than 'cupcake'! Why has everyone begun calling them cupcakes?