The purpose is to promote competition. (The requirement is under 215.371-2 Promote competition.)
FAR 5.203© begins, "Except for the acquisition of commercial items..."
Despite its exceptions, the resolicitation requirement is certainly applicable to many solicitations and, presumably, targets those where a problem was perceived.
There are two issues it seems to target (in the acquisitions to which it applies): (1) Contracting officers not complying with 5.203( B ), i.e. not establishing a solicitation response time that will afford potential offerors a reasonable opportunity to respond to each contract action for the acquisition of commercial items in an amount estimated to be greater than $25,000, and (2) requirements documents (intentionally or unintentionally) being written in a manner that does not promote competition .