Would you say HVAC companies are more or less "entitled" to that labor/profit, compared to, say, a company that prints business cards for those kinds of small businesses?
Any business is entitled to the profit they’re able to compete for and satisfy their customers, HVAC, lending, printing, whatever, even selling pictures of your butthole on the internet.
When regulation serves to limit via licensing and multi-year apprenticeships is where you get into market distortions that sometimes serve consumers and sometimes harm them. This happens to some degree in licensed trades (price out a drywall crew, painting or carpet [not licensed or at least licensed without apprenticeship in most places] vs a plumber, electrician, or HVAC).
When regulation serves to limit via licensing and multi-year apprenticeships is where you get into market distortions that sometimes serve consumers and sometimes harm them. This happens to some degree in licensed trades (price out a drywall crew, painting or carpet [not licensed or at least licensed without apprenticeship in most places] vs a plumber, electrician, or HVAC).