Because voters have figured out that voting doesn't fucking matter. Once you realize that a) the country has always been run by a single fascist bloc b) with multiple fascist factions fighting for control and c) fronted by two PR firms with subsidiary PR firms that drive psychological manipulation of voters into believing that d) this time it really is the most important election in history and e) voting will fix it and f) if you vote correctly then the fascists you put in power will stop being fascist and g) actually make structural change - once that becomes obvious, voting is just not something people are motivated to do. And to be clear even people like me who believe all those things vote in vast numbers because it is a ritualized symbol and it has implications in social situations and dynamics. And even still huge numbers of people just don't vote, which means massive numbers of people understand that the system is fully irredeemable.