government entities can get subsumed by politics and bureaucracy, while private markets can get distorted by poor regulations and anti-competitive practices. if bureaucrats can get thrown out for not being competitive with the private companies, and private companies can go out of business for not being efficient and serving customers well, we might get decent service-oriented entities in the market.
many goods that don't fit the simple paradigm of commerce (e.g., housing) can benefit from such a model.