Let me guess... to do the jobs that Americans won't do!
Those who just hate illegals are irrational. We cannot function without them. If you think otherwise you are just completely uninformed.
You are delusional. How then did America function prior to the 1990's?
In reality, American agriculture does well because of machines, Mexican agriculture where labor costs less than $3 a day can't compete with us because of machines --- it's the machines we have that allows the same guy who would make $3 a day in Mexico to make ten times that here.
There were lots of illegal Mexican workers here before the '90's. I lived in NW Oklahoma for a lot of years. A friend of the family had a job driving the bus(in the 60's) that returned illegals back to Mexico. He'd often tell stories of the recently deported worker beating the bus back to this side of the Rio Grande. In the early '70's, my uncle-in-law lived in one of those gated golf-course country club communities--upper middle class--outside Fort Worth. Nearly every member of the community employed a part-time illegal as well as the did the CC. Illegal Mexican workers have long been a significantly sized workforce in the US.