You are missing an important point: different systems fail in very different ways. The reason why people will generally prefer software over other ways of building things is because the cost of failure is often very low. No one is going to die if a website serves an incorrect image, nor will such a bug require billions of dollars worth of semiconductor inventory to be recalled to repair.

If every software project was run like an avionics project, software would be more reliable and of higher quality. But the world would be worse off; most of the software people use would never come into existence.