This is just a guess, but I suspect that "scale" also generally correlates positively with compensation. A medical device company with 50 employees just doesn't have the same resources as a company with 1M+ users, for example.

Following from that, compensation is one of the easiest ways to measure professional "success", which is why large, highly-compensated companies are commonly viewed as the pinnacle of software engineering.

Whether that's a fair or accurate assessment is a different question.