Why should this discussion be limited to out and out software companies. Think NASA. Think New Horizons. Think about the nuclear reactors and what would happen

Why should this discussion be limited to out and out software companies. Think NASA. Think New Horizons. Think about the nuclear reactors and what would happen to them when a sensor gives a wrong reading for reaching critical level. These are some pretty serious use-cases where Software Engineering processes are highly developed and rigourous. The computing systems used in a car itself (what do you think triggers the airbag on an accident?) can be trusted because of maturity in Software Engineering. Startups don't choose to follow these methods to keep costs low and stay lean. I say that in the broadest sense, because a banking startup will be different from your average SaaS startup.