Because the US had around 55% of all global manufacturing circa 1970 (with 130 million fewer people), due to its temporary quasi economic monopoly status after WW2 as the last highly developed industrial economy left standing.

That's why real US wages, stand-alone, have barely climbed in 40 years. Consider for a moment just how extremely high those wages were in ~1970, that it took decades for other high development nations to catch up.

That and the fact that healthcare costs over that time have soared in the US, so a big part of US compensation increases since 1970, have gone to employee health insurance costs (commonly anywhere from 10% to 30% of a person's compensation if you're near or above the median).