Why would stores be willing to lose money on some items they put on sale for Black Friday? *?

They don't necessarily lose money. Stores buy items much cheaper wholesale than they are selling them for, also they use Black Friday sales to shift some stock that has been sitting in the shelf for too long. They also know people come into the store for deals and those customers might buy additional items at full price while they are at the store and so on. Some shops also only make it look like a sale, but they marked prices higher before only to offer a "discount" for Black Friday. You still have to be careful and see if it's really a sale or not.