I saw this in my specialized science field too, in California a couple of decades ago. Real wages for that work have dropped 5 fold at least, partly due to automation, but I saw labs that were 100% immigrants, many H1Bs. Not complaining, just observing. were H1Bs necessary though? No. Many US born in that field found themselves jobless upon graduation. It was all about cheap labor

yup, anecdotally the majority of postdocs these days are internationals who are willing to work 60+ hour weeks on $50k a year, for the infinitesimal chance to land a R1 tenure-track faculty position. americans have no interest in getting a phd and then subjecting themselves to this kind of indentured servitude.