This is economics 101 - supply and demand. What everyone learns in their first course in economics. But most economists are paid to espouse a political perspective, so most choose to ignore it. Paraphrasing sinclair : When your salary depends on you not knowing something, you magically don't know something.
> - train people more. You hire them at lower qualifications, and educate them in house
When you prevent out sourcing, h1b visas, hiring illegals, etc, it forces local companies to invest in the local population. And it's not just at the company level. The reason we have a public education system, highways, public transportation is because the private sector needed literate workers and the ability to transport workers and goods. So companies put pressure on the government to provide education for the masses, build highways, public transportation, etc. Amazing what can be accomplished when private+public interests are aligned. When they aren't aligned, you get the rust belt, increasing wealth inequality and continued societal breakdown ( opioid crisis, late family creation, distrust between people and distrust of government, etc ).