It's all about money.
If truck drivers weren't paid by the mile, no one would drive tired.
If drywall hangers weren't paid by the square footage, I wouldn't have warped walls.
If my coworkers weren't given bonuses based on selling products, there would be no lying by them to make the sale. "Sure we will help you install a PCI modem in your computer. Be sure to call between x:xx pm and x:xx pm (when I'm not here) for the best support."
If EZ Lube guys weren't given bonuses for doing extra service to customers, this would not happen. I'm assuming they are given bonuses. Why else would they do something that's not required? To make the owners more money?