Safety is an important reason that low voltage AC E14 LED bulb has been used outside. Outdoor systems there will be maintenance as well as wiring that could get damaged due to outside elements. Low voltage is much safer than 120VAC or 220VAC if you are going to be working around that area a lot.
Low voltage AC E14 LED bulb allowed lighting designers to work with thicker filaments that do not snap as easy from mechanical shock or burn out. Low voltage AC lighting is used in many old systems.