I don’t think this is clear. They might just mechanise why have jobs when a machine can do the job just as well?

Illegal migration makes it infeasible to invest in technology to automate the work, because any business that wants to invest in automation will be undercut by a less ethical competitor employing illegal, artificially cheap workers. This also makes it hard to attract investment for companies building technology to automate this work, because investors assume that the government will continue to not enforce the law, leading to reduced demand for labor-replacing technology. We won't get significant innovation and investment in this field until the government sends a clear message that they will be consistently enforcing the law going forward.

If a machine could have done the job it would be doing it right now.

Not if using illegal workers is cheaper.

This assumes that a machine can do the job, but the present owners don't understand it. The article doesn't say "this will force farmers to mechanise more", see?