How is that self defeating from the programmers perspective? Code reviews can contribute to growth as a developer, ultimately helping ones career. When a developer desires such reviews, and a company is either unwilling or unable to provide them, why should they stay? There are plenty of other companies around to work at.

So suppose you met someone who graduated uni a year ago, was working as the sole developer at a non-profit, and wanted to learn to be better at recognising and writing well-structured code. Suppose they then asked you if they should stay at their job or go work for a company where they were working with other software engineers and you said they shouldn't. How would you advise them to develop their sense of good code style?

> I would be very surprised if someone could make a business out of 3rd party code reviews, but stranger things have happened.

Depending on how you define "make a business", this already happened. There are paid for code review and vulnerability scans. Sadly, I can't remember the companies that did them. I think one of them was by IBM... I saw them applied to new software (when it was nearly done) at two big, European companies. They were mostly worthless: The insights were barely above what Sonar gives you and many findings were "never gonna happen" edge cases.