Earlier quoted context omitted.
Have you seen modern plumbing? Solar heaters for water, grey water reclamation systems, hydronic heating, smart controllers for garden sprinklers. I've talked to quite a few very smart plumbers. The ones at the top of the field (earning good $) work with complex setups.
Majority of plumbing work (which also pays well) is still just fixing legacy pipework from old building that's decaying and needing repairs or replacements, not installing the latest heat-pump powered 'Butt-Squirter 2000', which still uses the same plumbing concepts of the last 100 years.
Does it? Last time I had major plumbing work done, a guy showed up in a very nice car (he no doubt earned very well) looked at what needed to be done and gave us quote. The two guys who barely spoke English and where on site 8-10 hours a day for a week actually doing the actual work probably earned considerably less.