When it comes to trades it's also a bit of "most people do not want to do this job because it's unglamorous"
Many people would choose not to be a plumber for various reasons. A shocking number of people seem to deem manual work as beneath them. Many others just prefer to do other work.
I have no problem doing plumbing or building. I've installed floors, ceiling fixtures, drywall, whatever. But I am best at software and would prefer to do that for my career.
