Why would an seo expert want to work for you instead of creating traffic/revenue for his own projects? Much better to learn the basics yourself and concentrate

Why would an seo expert want to work for you instead of creating traffic/revenue for his own projects? Much better to learn the basics yourself and concentrate on generating good content or some other compelling offer that will get people coming to you of their own free will. This will take time and will not be easy, hence why not everyone is already doing it.