Probably easier to have one non-changeable email/phone number in the firmware than have to modify/update it for every person they sell the car to.

Plus, it means the company gets to have a personal connection to all of their users, and when you're talking about a $100k buy-in, that might be the sort of attention a lot of these owners are expecting.

Same reason Apple doesn't let you copy individual files from your iPad to your iMac, you have to let Apple servers be the intermediary.