We long left the era where we "own" things that we buy. As everything is a computer now it has become very simple to control stuff that remotely that was working on its own before.

So the answer to "why would do this" is simply: "Because they can".

Every tiny decision is guided by increasing profit. No matter the side effects (short or long term ). Because with many shareholders administering pressure to maximize profits there's only one way to go (even if it's a dumb and shortsighted decision) maximizing profits NOW. If you are not doing that because you can see that increasing profits now will hurt profits in the future then you are hindering the project. You have to increase profits now, because if you are not then your competitor is doing it and that is a problem. If you are not going with the project you will be out of a job sooner or later. Then someone will take over that will make the decision you couldn't do.

This is a race to the bottom. Morals, integrity, honesty, responsibility and foresight are only obstacles in this logic (because the competition is not bound by them which gains them an advantage).

It's simply cheaper now to build everything in the car always and run an operating system that manages all these things and can control what you are doing in your car.

Cory Doctorow held a great keynote about this some ~10-ish years (?) ago with the title "The coming war on general computation" where he explained the side effects of putting DRM in every stupid appliance. The side effect here is that we cannot hack our cars to switch on the heated seats (or whatever other feature BMW is not allowing us to use for free) because of DRM. It is not "our" car, even though we bought it.