- liability
- hacking prevention: anybody in the car will be able to take over the car, so you should make sure there's always somebody you trust in the car
- regulatory: the owner of the car is liable for any infractions a car makes, so only there should always be somebody you trust in the car
But the wording makes clear that this is just a cash grab. You'd think that Tesla would have worded it to imply that they actually have a good reason...