Going back 30 years now, why do you think contractors, big and small, by the thousands, started hiring illegal aliens in the construction industry? They put hundreds of thousands of Americans out of work, drove 2012 wages into the 1980s, etc., etc.
They wanted employees who wouldn't bitch, who'd work for dirt cheap, and thought company benefits meant a 5 minute break. This is no secret.
Same reason companies like Walmart, constructions contractors etc, started using subcontractors in a big way years ago...The subcontractors hired the illegal low wage help, and fat corps like McDonald's, Walmart and construction bosses and many others would simply point the finger of blame at the subcontractors. A win win.
BTW, companies started cutting health benefits to employees, or providing near worthless benefits, en mass starting about 15+ years ago. This is nothing new, and it certainly didn't start under the current corrupt administration.
Big med and corrupt big insurance have been jacking up their their rates, which have been skyrocketing for 15+ years now. It reached a point where the average family was struggling just to maintain basic health insurance.
Blaming all this on the current government mobsters is bull chet. This crap has been going on for decades now.
My entire career was in the Chi Metro Area and nothing got done that wasn't done by a union construction worker (in this case it's good they are highly skilled). And there comes a point on a job when you know it's finally coming to an end -- when 'The Rock Goes Up', aka: Drywall installed.
And one day you notice, like out of the blue, the on-site radios switched from blasting Rock & Roll, Mo-Town and Blues to ... Mariachi! The Drywall jobs that 'kids' and Blacks used to do were now being done by 'Hispanics'.
This 'change' also crept to other areas of 'dirty work' -- Ditch Digging (not everything can be done with a machine). This Laborer job once almost all Black was 'now' turning Brown.
Luckily I never had to compete with these trades. So all our competing costs were pretty equal and this is where your Estimating experience came in [plus the 'intangibles' ;-)]. The only big unknown costs was what WC Ins would be due to how many claims you may have.
At one point there was only one GC who *tried* to use all Non Union Subs on his jobs that 'we' were on a select bidder's list of six pre-qualified contractors. The client finally got tired of that GC being picketed and 'disqualified him' -- his legal right (those were sweet times).
If any one group has been decimated by Illegals it's Blacks. Their once good & high paying jobs are now gone. Roofing would fall into this lost job category too.
I've had a 42 yr love hate relationship with the Union Construction Trades. But even today I wouldn't go into a 'big building' built by non union workers. Granted there's union jerks but they DO learn their craft during their apprenticeship.