Oil is just another commodity to these big store chains and the cheapest oil makes them the most profit.
They only care about price, thats the only way they can compete with the name brands. They are going to have an oil that meets min. specs but meeting specs and being as good as major brands is all to often not the same thing. If you want something better, they have the more expensive brand names to chose from. But they are counting on you being more interested in price and buying thier house brand especially when they imply or let you assume its made by a well know company, so it must be the very same.
So, who makes it means nothing. People assume because name brand X makes this product its the exact same as the same prodcut name brand X sells. If you believe that, you could wrong 100% of the time.