"The reason is so they can keep monitoring your car and using your data against you. "
How?
Well, without hijacking the thread and turning into a privacy discussion, I for one am rather sick and tired of everyone and their brother using my data for their own purposes. Phones, thermostats, tv's...everything.
Well onstar is certainly not as sinister as google, rest assured, they're using that data to figure out how to extract more money from you in the name of "making your life easier" SOme of which is ok and most might be willing to pay for or get something for free in exchange for it. . Alot of it is not. . Your driving habits, where you go, how often you go, if you use your garage door homelink, how you use your door locks, how fast you go, when you go how many people are in the car, how you used your hvac,. All that data is being collected and will be used at some point to decide if they can charge for it somehow, sell you an ad, or worse, hand the data over to govt (no I'm not a consipircist, but this is where this data generally ends up) or something to that effect.
If you read the onstar gig carefully when you bought your car it was more or less required and says in the agreement, as long as your have AN account, they can query your car and take the data and then it's their data, not yours.
So, for instance, in the future, hvac might be locked out from your control in the name, your not using it efficiently enough, the ai engine analyzing the data, or worse, govt , might say, yeah, your not allowed to have high heat because it's an environmental action day where we don't have enough juice to serve the people. Or something to that effect.
No I'm not paranoid, I'm just a fan of my data is...my data, my driving habits are, my driving habits, not GM's or anyone elses. As much as I can keep my data mine, I try to.