1080p stream in acceptable bitrate is around 1MB/s.

I think most of the privacy-violating and abuse-facilitating scenarios that we're all too plausibly imagining could be served by the transmission and storage of even a single photograph per drive.

Why would car manufacturers even consider doing that? What is the purpose?

All of the existing consumer-surveillance tech seems to be focused on 1) Finding ways to make your attention more valuable to advertisers and 2) Selling information on your movements and proclivities to interested governments.

Pictures from inside a car could fit right in with those priorities. They could tell car makers, advertisers, insurers, and governments a lot about who really drives the car the most, that person's demographics, taste in clothing, driving ability, distractability, fatigue levels, health issues, etc.

I should be clear: I'm absolutely speculating. But I don't know how anyone might look at the landscape that exists today, with surveillance in our phones, our televisions, our music players, and our cars, and think that such speculation is far-fetched or unrealistic.