Except with insurance they probably made money. The trick is for it to happen often enough that insurance gets too expensive.
Well insurance only pays out on the value the retailer bought their inventory for, not the sticker price. Yeah they’re getting a lot of money but rebuilding inventory and a new warehouse is probably more money. And Insurance companies might start considering underpaid employees as an insurance liability.
Assuming it wasn’t a company owned warehouse, the landlord will probably be making an argument that their disgruntled employee makes the fire their fault.