Which is to keep the evil hackers out, but has the additional benefit that they can have a captive market for a $100 part that would normally be $1. The aftermarket suppliers are locked out of the market because they don't have the private keys to handshake on the bus.

(happily keeping my late 90's car running, although my most recent car literally has gone 100k miles with _NOTHING_ but oil, tires and brake pads). Its now at its first service interval and I'm wondering if I should just trade it in before anything breaks.