Farming, construction, landscaping, etc all need undocumented labor over 'legal' labor, all around the country, but especially in farm country. Do you really believe that they honestly do not want migrant labor coming over the borders?
No payroll taxes/benefits, and undocumented workers are much easier to exploit. They are highly unlikely to go to the cops about anything criminal that happens on the job, or to OSHA about any workplace safety violations, or to the district attorney about wage theft, and so on. They fear getting deported or tossed in jail. They're also socially isolated by various barriers - language, racial prejudice, and so on...so word of shady stuff going on is a lot less likely to make its way out. Don't want anyone to find out about your toxic waste dumping? Have your migrant workers do it.
Also, migrant workers will do a lot of shit jobs that a lot of Americans just don't want to do, or at least not at fair market value labor rates that the business would be "sustainable" at.
Meanwhile, politicians shout about how that migrant worker is stealing your job and so on. So they get the $$$ from the people who want exploitable labor, and the votes from the Pickup Truck Petes who think those "illegals" are "stealin' our jobs" and so on.
It's not far off from why education is so poorly funded and constantly under various attacks in the US. There's a lot of wealthy people who want easily manipulated, uneducated, trapped-in-poverty workers to exploit. This is also why abortion is under constant attack; access to family planning is a huge factor to people escaping poverty.