your brain may have associated the reward with the parts of the process that involve walking to the store and the purchase, rather than just the consumption
My initial thought is that it’s a form of mindfulness.
Angus Pauley

This could be a big part of it, actually. Have you heard of the power of variable rewards to strengthen habits? It’s how Facebook’s newsfeed is so addictive. Every time you I go to the discount bakery, there’s a different item on sale. There’s a variable reward. With the hot-cross buns in the cupboard there’s none of that.