Isn't the main reason just that failures in the vast majority of software aren't that bad? Like if you build a bad house it could collapse and kill someone. If you build a bad calendar app/email client/text editor it might... be a bit difficult to use? Crash sometimes?

And then people wont use it because it's bad and your company will go under, problem solved. Some other 20 year old (or 40 year old) flying by the seat of their pants who happens to be good at development will step in and build something that works.

Obviously if you're building medical device firmware, or aircraft control systems or whatever then it's a whole different story. But generally companies building that sort of thing do have a much more systematic and dedicated approach to quality. And there are industry regulations that enforce that.