Some of us make choices that are not based solely on how cheap the product is. I don't have Walmart in my hometown, and would rather my sales taxes go to my local government instead of enriching neighboring cities.
Also, if you have a DG Market, basically a DG with a full grocery store inside, you may find their prices largely competitive. The selection, less so. But I compared a few staple items recently to see how they're priced against our nearest Walmart (20 miles away), and our DG Market is right on-par.
Important to my recent habits, DG Market beats pretty much every other grocery store on mineral water. I buy the stuff from the Mexican food aisle, Mineragua. Lately, it's 3 for $3, which keeps me in fizzy water for the better part of month. That price isn't touched by pretty much any other store (most don't even carry Mineragua), except maybe Aldi, where everything seems to be cheaper than anywhere else. But Aldi also is 20+ miles from home, so the deals are often not worth the travel time and expense.