In any business, if you have the volume then it's easy to subsidize the loss. My small shop does a standard oil change (up to 5 qt, with fluid top off, vacuum, window wash) for $36 OTD. I think. Maybe $34. Either way, that price barely covers parts/labor cost. Maybe $1-$2 profit per car, assuming the customer doesn't buy any add-on's. We also don't charge labor for air filters, cabin filters, or light bulbs in most circumstances.
Any shop knows that there's very little money to be made in a quick lube, but like others have said it's not about the dollar amount of the oil change itself. It's about up-selling maintenance items, flushes, brakes etc. That's where revenue comes from.