You still don't get it. The dealership has a labor rate, which they are probably charging 1/2-hour for this replacement. But that covers the cost of the service rep who sells the repair, the guy who drives your truck into the shop, the service tech who makes the repair. It also covers that cost of that paper and plastic they put on the seat and floor. All this is in addition to maintaining a profit and keeping the lights on.
You have the ability to do it yourself (as do I), but a lot of people don't, won't, or wouldn't know where to start.
Imagine going to a restaurant and buying a cheese burger for $14 when you can make one at home for about $3 - $4.