Because this completely dis-incentivises companies to spend money developing features in the first place, and makes it impossible for them to recoup the sunk cost of development over car sales, since they're competing against companies who did not pay those costs.
It seems to me what's unsustainable is relying on a system built on trade secrets. Something we quickly moved away from in the software world, which has greatly accelerated development, been mutually beneficial to everybody, and certainly hasn't been "unsustainable".
I remember someone comparing, on HN, what "closed source" is to science to what ancient guild secrets were to alchemy. Are guild secrets any more sustainable than closed source?
It's completely unsustainable.