walmart needs to understand that it oversees a circular flow of paper money. as they are frequently a major employer in the areas they exist, the wages they distribute come back to them either directly or via multiplier effects. for walmart to eliminate wage slave employees would force them to close many of their stores, where the walmart is the centre of the local economy.
that's less true of any specific fast food restaurant or other low wage business, but is in aggregate. the walmart is not unique but is special, as it generates aggregate effects.