We can find countless examples of high paying jobs that are absolutely useless to our industrial civilisation. The answer is likely a mixture of both: salaries

We can find countless examples of high paying jobs that are absolutely useless to our industrial civilisation. The answer is likely a mixture of both: salaries are not that much correlated to skill and value overall, and some industries have much lower margins than others. Having to compete with the likes of Airbus and ULA for workers, SpaceX doesn't need to inflate the salaries that much to get top talents.