If I was homeless in LA, I still wouldn't work for 16 bucks an hour in the hot sun around dangerous chemicals with no benefits in the middle of nowhere.
In my country, you can work in a warehouse. You get job security, full health coverage, and 18 per hour. There are worker safety regulations that actually get followed, regular breaks, shade, and ppe provided if you're working with dangerous chemicals. You're not out in the sun all day. The US agricultural industry can't provide any of this. Why would anyone work for them if they weren't a poor immigrant planning to take their wages back to Mexico, where 16 is at least a living wage?