The answer can be found in the regulatory history that is referenced in the brackets below FAR 10.003. See 76 Federal Register 14562.

The reason for the clause appears to be directly tied to a directive from Congress that is set forth in Section 826 (Market Research) of the National Defense Authorization Act for FY2008 (Public Law 110-181). That law specifically required that an acquisition regulation be promulgated by the FAR Council which requires prime contractors, who enter into a contract valued in excess of $5M with any executive agency, to conduct market research to determine whether commercial item subcontractors could assist in the provision of supplies or services in excess of the SAT.

Note that similar requirements, which provide that prime contractors providing “other than commercial items” must seek out commercial item subcontractors “to the maximum extent practicable” to assist in providing supplies or services to the Government, can be found at FAR 44.402 and 52.244-6.