A lot of people might not vote because they are content and don't really see it impacting their daily lives. Voting is not popular like sports are because politics for a lot of people is just plain boring. Being a politician doesn't have the glamour of being a celebrity. some people might also be discontent by politicians being a lot of talk with a lot of inaction or opposite actions of what they said they would do.
Maybe try giving people financial incentives to vote. People love the prospect of free stuff. enter everyone who votes into a lottery and draw prizes or just give them lottery tickets. I personally don't like to gamble but a lot of the people who don't vote might and the possibility of winning something just might move them to the polls. Maybe some sort of tax break but that seems like it would be complicating things.