Manufacturers are not interest in maximising their social benefit: they want to maximise their profit and this is done by producing fewer items but at a higher

Manufacturers are not interest in maximising their social benefit: they want to maximise their profit and this is done by producing fewer items but at a higher price (to be technical, a monopoly would produce until marginal revenue = marginal cost). Manufacturers can set recommended retail prices but their are limitations to how these can be enforced.