Haha. $20/hr plumbers hilarious. I am sure you can't, but please provide a link to this source.
https://money.usnews.com/careers/best-jobs/plumber/salary
When the data disagrees with your mental model, consider re-evaluating your mental model.
The amount a client pays per hour for labor != the takehome pay of the person whose time you're ostensibly being charged for.
Revenue is not profit, and "price per hour for labor" != "hourly rate I pay my laborers". This is even true in owner-operator businesses. Furthermore, in bursty markets, "annual income amortized over career" != "my hourly rate multiplied by 40-60 multiplied by the number of weeks I want to work".
The numbers from my links are INCOME, not "what the business charged the client".