one take: if the government offers a higher wage but still lower than marginal productivity, a profit-maximizing (former) monopsonist raises its wage. the worker then is only actually lured away if the government offers a wage above the true opportunity cost, presumably because the work is worth it.

(in a cost-benefit analysis, analysts unaware of the labor monopsony might erroneously judge a program worthwhile by underestimating the costs that would actually be required to hire the labor.)