As I understand it, for years AF operated Concorde only because BA continued to operate Concorde, standing a loss of the equivalent of tens of millions of Euros a year - French pride would not have allowed a unilateral retirement while BA continued to operate the aircraft. PAR-NYC was more expensive to operate than LON-NYC, if for no other reason than that it's a longer route - hence Concorde was much more often load limited on PAR-NYC to the extent that some (8?) seats were ultimately removed from the AF aircraft. And in addition, the ultra-premium market was always much smaller in Paris than in London.

I suspect that the different attitude to promoting the aircraft probably stemmed from the AF view that Concorde was a pretty white elephant, whereas for BA she contributed positively to both image and bottom line.

Eventually, a combination of falling revenue for BA (eg poor economy, lost customers on 11.09.01) and rising maintenance costs all round (eg cockpit door mods) made it possible for AF to kill Concorde by a unilateral retirement and withdrawal from the maintenance programme, as the residual maintenance costs were then high enough to make it uneconomic for BA to continue on their own.