they just want to Pay them less, and no benefits. so they can reap in all the profits. plus its also harder to exploit a citizen, because they will start reporting the farm owners for unfavaroable conditions, or bring the press(news) on them, plus they would ask for benefits and a higher wage, which they deserve. migrant workers arnt going to do this.

also the fact that other jobs pay better, and its not brutal on the body. even places like walmart, target,or some warehouse, or grocery store workers have better pay and not working brutal hours/physicial labor.