The Bracero program was ended, but the H-2A visa program for seasonal farm labor remains active, with no numeric cap and hundreds of thousands of visas issued each year. I don't blame workers for making a living, but is there some reason why these business owners requiring seasonal labor could not obtain the proper visa for it?
It's actually better in many cases for businesses to hire undocumented workers, since it makes the workers position much more tenuous. They are much less like to unionize, demand higher pay, etc. if the threat of deportation is hanging over their head
Friction of paperwork. Not saying it's right, but it's a reason.
Also, you are shifting the blame for immigrants getting arrested to the owners. That means the employees are actually blameless: they are caught between seldom-enforced laws and a need to thrive and feed their families.
They can pay them less, treat them worse, then if there are any issues, deport them. It's very gross.