If lack of people who are willing to do a job or are able to do a job means better pay for those do and can, then why are pressman paid so little?

I started running printing presses at 13 years old. I have yet to meet any other pressman. Have met teachers, pharmacists, auto mechanics, nurses, doctors, lawyers, computer engineers, welders, strippera, roofers, painters, bankers, dermatologists… You get the idea. Nobody seems to know how to run a printing press though. Every business selling a product wants their product to have images for marketing. That requires someone who knows how to run a printing press. Why are pressman being treated as if they are working the register at Staples instead of being paid properly?