It is just plain laziness. I had my dealer claim that the headlights were not adjustable because they were self-levelling
This is a little more involved. I don't think a dealer is going to take the time to research the answer, be it Hyundai or BMW or Mercedes. That is why they quoted you the $6K price, it was a get you out of their hair quote.
Either you or a customizer are going to have to pull the physical and electrical specifications of the two seats and compare them. There is an airbag in the seat, but I would suspect that it is the same one for both seats. You will have to dig out that information. In the long run, because of the airbag, I don't think any dealer will touch that mod.