The referendum was based on a set calendar. The French central government refused to have it rescheduled. The Kanaky nationalists were opposed to having it run in the thick of COVID. The trajectory was in their favour, based on previous referendum outcomes, so I'm inclined to believe they boycotted as a matter of principle. In the end, the people who voted were mostly settlers from Metropolitan France, whose representatives are now actively working to roll back Kanaky autonomy. This information is very easy to find for anyone who cares, so I'm (genuinely) curious why you'd ask in what seems like a casually dismissive tone.