Welcome to the world of business. Retail space is so obscenely high, you have to move a lot of coffee and donuts just to break even, let alone turn a profit.
Then in the case of Dunkin Donuts, you have overhead, franchise fees, paying employees, local and state taxes, etc etc etc.
Then after all your expenses are paid, THEN you get to keep what's left.
If you keep a dime out of every dollar, you're doing good.