Again, you seem to be stopping the story at the wrong point. The initial job is to find out whether the project is worth investing in. 9 out of 10 startups fail

Again, you seem to be stopping the story at the wrong point. The initial job is to find out whether the project is worth investing in. 9 out of 10 startups fail, they say; if you're in one of the 9, you need to know that ASAP. If you can tell that with throwaway code, great! You've saved a shit-ton of money. As an example, I did a startup circa 2010. We raised money on an idea that VCs were very excited about. So much so that we found out later that other VCs had invested in similar notions. We spent a few months building disposable prototypes to test the value prop. It turned out that users hated the idea no matter what we tried. So we killed it after spending maybe $100k and did something else. Job done! But the other companies persevered, building full apps, and each burned millions before they realized there was no future in it. So in that case, yes, you don't want to invest a lot. But a few ideas later we had something that looked to have real product market fit. At that point, we threw away the code and started fresh with solid tests, CD, and other quality investments. Why? Because the job we were trying to do had changed. It had gone from hypothesis testing to actually serving users and building a real product. If you want to get that job done well, you can't afford to have a garbage code base.