I don't know why it happens. It might be that you burn so many calories cycling that you are actually hungry or famished when you return. When I get a craving for sweets I try to reach for really ripe fresh pineapple, cherries or blueberries, dried figs (dried fruits have a lot of sugar in them) or apples with Nutella. Also, sweet potatoes with cinnamon . . . or really dark chocolate like Dove Promises. Dark chocolate is actually healthy in moderation. In winter, hot chocolate (with 2 dove promises) is my favorite after exercise treat.
Sandy