This seems straight up protection for their service centers profit.
While Elon has said they don't want them to be profit centers, the cost and pseudo-requirement of annual service is evidence that is not the case. While, like many things there are multiple reasons for it, and I'm sure not wanting to deal with the negative publicity that would occur if an indy/home mechanic hurt themselves, or broke the car is certainly occurred to them. I bet its more an issue of the right hand not talking to the left, where what Elon says in public is not what is actually set as corporate policy.