Maybe they have always done it like that in Japan ffs... How is dying sweets extra? It makes sense, and its smart. Idk where you live but caramelised apples in most places are dyed, the red is not natural.
Because its fun. Because making food into different colors is a festive tradition. The vendors do it to make their stores fit in to the festive theme. That's not a hard concept to grasp is it? Btw, Japans food dye is made from seaweed, crushes flowers or vegetables. They don't have the harsh chemicals like we have back in our food dye in the US, so they don't have to think twice about using food dye. So they get to enjoy food in different colors, and the food is technically is natural because there's no dangerous chemicals in them.
Green apples aren't made with food dye lol