Almost every major platform I can think of was slow to provide what it's innovation community wanted - I remember giving countless apps my Twitter or LinkedIn passwords in order to access 3rd party functionality and value. Blackberry/RIM held a frightening number of email address and passwords in order for the service to work.
But there's something very uncomfortable about surrendering my EV's credentials to the point that I just won't do it.
I bristle not only at giving away access to my current location but also where I'm going. I don't especially like the idea of Tesla having all this data but I'm certainly not comfortable with small startups having it.
In the event that security is compromised there's also too much opportunity for mass-griefing and inconveniencing - locking me out of my car, heating my car at the highest temperature (I won't go on, but you get the point).
My take is that the engineers at Tesla know how to build OAuth - they intentionally are not doing this because the company is not ready for this world or prepared to accept it - yet. By requiring you to give away the farm with your username and password it maintains a high stakes 'all or nothing' which I'm sure they hope will put off most of their customers.
Give it time, but once these companies do have petitioned permissioning I'm not sure what the value add will be for these startups like Telematica.