[BigAls87Z28]

the same reason why a steak that cost $11 in a supermarket will cost you $30 if you go to a restaurant. It's all about the convenience. you are paying for a service and not just the cost of parts. Now some shops will allow you to bring your own stuff, but that would be like bringing your own food to a restaurant and have them cook it for you for a small fee. This is how business is done. You don't complain about anything else in your life where the business has to pay less than you do so why are you now amazed that this happens in the automotive service industry.
if you are that worried about paying a markup for a part and you should start to learn how to do it yourself. If you didn't have the time or the know how to do it then that is understandable. But do not get upset when you find out that the business is trying to make money.