ISA Leading Development of Electric Energy Operational Technology Security Profile for IEC 62443 Standard

Would be interesting to know why US DOE CESER chose to endorse the IEC 62443 Cybersecurity Framework when many US Electric Grid Operators have already implemented NIST's Cybersecurity Framework V 1.1 and related NIST standards covering the software supply chain SP 800-161r1 and cybersecurity guidelines for ICS/OT environments: SP 800-83 R3