If the state or employer is required or expected to supply additional benefits to people working abroad, the benefit to the state or employer in substituting workers with less ability (legally or otherwise) to claim or obtain those benefits is even larger than it might be in-country. (I'm ignoring the obvious issue of it potentially being less legally or politically easy to handle here as the parent comment does not mention these at all).

It sounds like you have an anecdote about some people you know working on these projects, but the details that seem intended to imply that it's unlikely that _any_ people working these projects are Chinese prisoners actually imply the opposite.