Unwilling humans, and humans getting paid less than the cost of their legal ruin, are a liability to criminal enterprises. Those humans are at risk of tattling. Yes, such enterprises can invest in buying prosecutors, prison guards, prisoners, etc. to punish tattle tales -- but robots don't talk. Sure, maybe parts can get traced, but it's bound to be easier to "secure" a part supply (make them yourself if you have to) than to "secure" your human liabilities.