Why? It's a BA initiative not a oneworld one, over and above BA's oneworld obligations - just like the Concorde Room is not a normal 'First Class' lounge in the sense that it's not open to BA Golds or Emeralds. It's a BA-specific lounge only open to ticketed F pax/BA 'specials'. (That said, I too was previously under the impression fast track was ticketed J/F only, no status advantage even for BA's own cardholders).