In retail this is called a loss leader. However, the low overhead of the service probably contributes to the lower cost as well. This isn't their main business

In retail this is called a loss leader. However, the low overhead of the service probably contributes to the lower cost as well. This isn't their main business and Walmart already have TONS of locations, they don't have to pay rent or commission on physical locations nor do they have to pay for labor, the employees would be there anyways. It doesn't cost them hardly anything to add this service to their main business.