Because people think that their vote doen't matter much in a larger population.Moreover in the 3rd world countries the government is decided by uneducated ones as they are easy to get bribed where the educated ones vote less for the same reason.People should come out and vote so that they atleast shouldn't blame the outcome and be a good citizen.Their are many incidents where the leaders got elected or defeated by just one vote.So individual vote matters in my opinion.