A fuel policy that pushed things to the very edge of the legal limit with no thought whether this was sensible (aerial work so no alternate). A pilot who pushed things even further (no OEI). A sense of complacency (not getting en route weather and not monitoring a deteriorating situation). Possible difficulties at Noumea. Poor CRM (not asking FO to check calculations).
How else was this going to end up. This all reads like a recipe for disaster. In the end they got themselves backed into a tight corner.
There is more than enough blame to go around. The crew did the wrong thing, but they were not the only ones.