We also have trash picked up by prisoners, but I haven’t seen the field workers in years. I admit I was pretty shocked the first time I saw it - they were shackled together pulling weeds I think.... I was driving so I didn’t have time to watch for long.
We don’t use shackles, and the only ones who do this are sentenced by the courts to weekends in jail and the menial labor. DWI and other assorted convictions, but not “hard” criminals. I encounter them at the fire station where they often work cleaning. If they walk away, they end up back before a judge with fewer options. Maybe straight jail time, so the weekend thing is preferable.