They will use any pretext to rule. Not voting doesn't send any more of a message to the ruling class than voting blue no matter who. It's more about sending a message to the masses. Chipping away at the legitimacy of the "democratic" institutions and making it blatant that they actually rule by force rather than by consent. For the same reason, it is not a program for revolution, since they rule by force anyway. You won't dismantle their police forces and armies by chooming on the couch. But it does make the whole media commentariat look like fucking clowns when they celebrate their mandate garnered from 5% of the population. It makes insurrectionary movements look that much more legitimate by comparison.