Immigration in USA has multiple components, but it seems to be you're undervaluing the amount of opportunistic intellectual workers, who come here to participate in high level education, and entrepreneurial capitalism. But, here are the numbers across multiple sources (thx GPT):
- High-skilled (H-1B + EB green cards + PhD retention): ~200–300k annually.
- Low-wage (H-2A + H-2B + others): ~500k+ legally, probably >700k when including unauthorized inflows.
This a pretty good amount of brain power absorption, not just farm work.