They know alot. The data is used to estimate average speeds on roads with alot of throughput and can profile location between known sites. (Work/school/etc)
You can buy data about the incomes of people driving past a given intersection. That's why you'll see a Starbucks sometimes on a trunk road in a sketch area.
Yes, the aggregate value of this data is substantial. And of course nobody in the possession of something valuable, especially not a telco, ever thought 'am I acting in the interest of the data subjects by selling this data?'.
You can buy data about the incomes of people driving past a given intersection. That's why you'll see a Starbucks sometimes on a trunk road in a sketch area.