Why didn’t she also open the Sydney Games?
I imagine the organizers decided not to invite her. She does not have to open the games and in the case of Sydney 2000 her representative the Governor General opened the games. Also Melbourne 1956 only Phil showed up. For Calgary 1988 and Vancouver 2010 the GGs at the time opened the games. Curiously for Montreal in 1976 the separatist opposition leader for the Quebec legislature sent a letter to the Queen asking her not to come to open the games but since he had no standing she opened the games because she had been invited to. She has a history of doing her duty even in the face of opposition.