The US is one of the biggest money earners for QF.
If J* was to fly to SFO either via AKL or direct with another aircraft it would have a detrimental effect on the bottom line of QF.
The money saved would easily pay for a cheap ticket from SFO to LAX or anywhere else in the US.
This might be another rumour but if J* is to be utilised to it's best potential it should be used on flights that complement the QF network and not compete with it.