I think the GP is implying that Home Depot might have lost money on the sale because the delivery probably cost them more than they earned from selling the light bulbs.
For Home Depot, assuming it's not a mistake, that's probably an investment in persuading customers to look to them first and not shop around.
For Home Depot, assuming it's not a mistake, that's probably an investment in persuading customers to look to them first and not shop around.