Re: TL:DR Security by obscurity is good for you. Don't bother your silliy heads about such things
Cars are a good example IMO - there's a lot of software in them these days controlling the full driving experience. I have no idea how the engine management system in my car works, nor do I particularly need to know, but it's there to manage fuel consumption and emissions and make sure that the injectors open and close at the right instance squirting the right amount of fuel in. If the ECU or one of the sensors that feeds the ECU breaks, then the engine might fail, or emissions may go illegal and the little spanner lights on up the dashboard. It's this issue around the engine software that caused the large VW emissions fall-out.
Then there's all the other things (auto breaking, line detection warnings, auto parking, ...) that cars are increasingly able to do. Most of these probably don't have much complex choices in them, but we trust that they work, and can guess how they work (for each of the examples I gave, then that's radar, opto-electronics, and magic).
Some of these would be better made public (especially following the emissions scandal); but I can't see companies that have developed (say) auto-parking wanting to share their code as this removes a commercial advantage from rivals that don't have it. It's the sort of thing that could be shared at a broad level, but that probably wouldn't count for much and it's the detail that usually matters.