The difference for me is control. On a phone you get per-app permissions, you can switch location off, and you can leave it at home. The car's telematics modem is always on, there's no permission screen for it, and you usually can't opt out without losing features you paid for.

It's also not hypothetical: in 2024 GM was reported to have shared drivers' trip and hard-braking data with data brokers that fed insurers' risk scores, and the FTC later took action over it. People saw premiums go up without ever knowingly agreeing to it. That's why folks pull fuses: the phone at least gives you a switch.