Why are requests for proposals (RFPs) used?

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I see, this is very helpful.

First, they may be mandated by the legislation or regulations pertaining to contracting, but, even if not required, they can serve as a means of stimulating the development of needed resources. Also, because an RFP appears to conform to the norms of rational planning, equity, and “good government”, it may enhance the credibility of the governmental agency as an organization that is committed to fairness, efficiency, and accountability.