People can care and think the two candidates with a chance to win are too bad to endorse with a vote, leading them to stay home and spend their time more wisely than in what they might consider to be a farce of democracy.
They may also live in an area where their preferred candidate has no chance of winning, making their vote a waste of time.
Of course it makes a difference to vote for what you actually want, no matter if they win this time. If you don't have an appointment at the euthanasia office and you (or someone who can vote in your name) is in good enough health to reasonably go, I can't (currently) think of an argument why it wouldn't be worth one's time to vote for who should govern you
They may also live in an area where their preferred candidate has no chance of winning, making their vote a waste of time.