This Cracked video on myths about voting hits it on the first item.
Politicians give rewards based on how much you can help them. This means that in Democracies they give (some) rewards to voters. (This is not a bug of Democracy, it's a feature.)
The rewards are related to the number/percentage of votes in a demographic but the relation is not a strictly linear one.
Why was not cutting Social Security/Medicare the one big thing that Trump and Clinton agreed on at the debates? (Even if they didn't agree on how they'd pay for them.) Because old people vote more than other demographics.
If you want your concerns addressed by politicians then you need to vote. In this context it doesn't matter who you vote for. It doesn't matter if the person you voted for wins or loses, and it doesn't matter if you're just the Nth "unneeded" vote for someone who was already going to win in a landslide.
After the election both sides will be looking at the turnout, and they'll base their policy decisions at least partly on those numbers.
If young people started voting in the same numbers as old people then for the next four years both sides would find reasons to start supporting things that matter to young people the same way they support Social Security and Medicare.
Finally, here's a "reward" for making it to the end!
The Epic Rap Battle Trump vs Clinton video! (Just in case you didn't already see the link i posted on Twitter =)