"Back-breaking" isn't just a figure-of-speech; modern medicine isn't (yet?) advanced enough that a rational actor should ever choose construction work over something else; and there are just enough desperate people around that I doubt anyone is willing to pay the true cost of construction-work to a not-as-desperate would-be construction-worker.
The limited resource here, then, is actually: desperate people who are still smart enough to do construction work.
I can't wait until construction becomes a non-human-powered activity - even if it still requires a human to control the machinery.
That trend is so powerful precisely because lots of trade-working parents don't want their kids to suffer the kinds of medical bills, chronic pains (with potential resulting opioid addictions) and stunted healthspans, that they do.
Granted, construction is rather especially bad among the trades in this manner: things like welding are not quite as physically-demanding.