>What would motivate Apple to interfere in a third-party relationship business between the Developer and Tesla

Who guarantees there even is a "third-party relationship business between the Developer and Tesla"?

Should Apple let any app that claims to have one or be officially sanctioned or whatever dupe customers?

In contract law, “third party” is a term of art meaning a party which is not a party to the contract. So the fact that Tesla is not a party to the developer’s agreement with Apple makes it a third party.

>In contract law, “third party” is a term of art

Next thing you'll tell me there's a Sanity Clause, with little elves helping him, etc.

Yeah, I know. My question is: "who guaranteers that the app maker has any agreement with Tesla"?

One could release an app claiming so, without Tesla approval, and do shady stuff -- where Apple gets part of the blame from customers.

Legal security? Theoretically Tesla can go after Apple for permitting 3rd parties access to Tesla’s APIs. AFAIK, API access to Tesla’s cars has been reverse-engineered and isn’t something Tesla publishes themselves so there could me DMCA issues, too. Not trying to state what is actually legal or not but rather Maybe Apple is trying to play it real safe.

I guess on top of that Tesla could stop supporting the API any day, creating a bad user experience.

That literally applies to something like 90% of apps.