Yes that is how things work in the real world. You pay money to get something. Your statement "that adds another $9-15 to the cost of that $20 a month cost" is not true because you get more for what you are paying for Amazon Prime than just the opportunity to subscribe to your local Fanduel RSN…unless you are only getting Prime so you can get that local RSN from Amazon.1. Your Benefits of Free Shipping, is NOT FREE, its part of the Amazon SUB.
2. Amazon is not offering the service, they are simply a place to get it. They pass on what they get from MLB.TV I would imagine, I don't believe they have anything to do with Producing the games.