The Cheeseburger Has New Complements

Who would imagine that a complements for cheeseburgers would be a Krispy Kreme doughnut?! It seems to be a little far fetched and unappetizing to me, but the sales are booming. Many people think of complements like chips and dip or peanut butter and jelly, not cheeseburgers and doughnuts, that's what I would consider a substitute. Now new supply and demand graphs need to be made showing the demand for cheeseburgers and doughnuts rising together not a trade-off between the two. Seems to me nowadays the things we considered substitutes in the past will now actually turn into complements in the future. What do you think about these new complements and their sales?