Good point, but how much of that is the manufacturer pre-compensating itself for all the extra maintenance that it won't sell you?
I can take pretty much any kind of car to my local independent place - which happens to be less than 1/2 mile away - and they'll fix it for me. They'll stick to using original manufacturers parts unless I instruct them not to. If they think something ought to be covered by warranty and so ought to be looked at via the original manufacturer's servicing network, they'll decline the job and tell me why.
It's hard to imagine a system with less lock-in!
How much does Tesla pre-compensate for the maintenance they won't authorize others to do?