I doubt they are selling at a loss even at the low price lol. It's like
parts stores and auto mechanical shops. It's generally accepted that there's a 30% markup from
parts store to mechanic shop (the price they sell you the part for). The
parts store typically delivers the part, and the only time involved for the mechanic shop is the call to order the part. The part store has easily 30% mark up from what the business pays for the part, it's probably closer to 50%-100% markup. It's just how business works, every set of hands something goes through is anothe set of hands that needs to make a profit to keep doing their work. Ideally the best price you could get is buying direct from the manufacture, but they don't normally care about single item sales, they want to sell 1000 units at once. That's how the distrubution network works, they buy in bulk, then sell in smaller quantities to stores etc that can accept say 20 units each, then the customer buys 1-2.
I've personally hit this wall myself, the connector to make the 84-85 round CDI adapters I was able to get through the guy I'm working with in the past, but his source closed up and now we have to order like 5000 qty min order. Price is a lot better per unit, but 5000 connectors for a very niche market is very very hard to invest in with out putting a huge markup on the connector value.
Anyway, the online walmart store is more like amazon, there's more than one seller, and they can choose whatever price they want. The person selling the cheap priced tires probably ran out of stock, so it's the next best price from the short list of sellers.