> if Walmart didn't employ these people

Walmart earns $13k of profit across each of their 2m employees. One could make the argument that if Walmart had to pay each employee an extra (say) $3k annually [1], management would instead choose to shut the whole thing down and return capital to the shareholders, which would be a choice available to them. But I don't find that argument compelling in the slightest, and Walmart does not have any compelling IP that would preclude letting management shut it down and have the likes of Target/Kroger fill the gap in the market.

1 - an additional $3k annually would be transformative to the life of the average Walmart employee.