Decent returns aren't enough for a risky investment, they need to be spectacular returns.

The benefit to the country as a whole is potentially large, but most of it wouldn't show up as profit for the company itself. I'm sure it would do quite well if it was successful, but the benefits to car manufacturers and to having this sort of technology on-shore would not translate into monetary returns on private investment. That's the sort of thing government intervention is good for.

I think it is in certain very limited circumstances. The Space Shuttle's software seems like it was actually engineered. More generally, there are systems where all the inputs and outputs are well understood along with the entire state space of the software. Redundancy can be achieved by running different software on different computers such that any one is capable of keeping essential functions running on its own. Often there are rigorous requirements around test coverage and formal verification.

This is tremendously expensive (writing two or more independent copies of the core functionality!) and rapidly becomes intractable if the interaction with the world is not pretty strictly limited. It's rarely worth it, so the vast majority of software isn't what I'd call engineered.