Peer pressure (and used to be beer pressure)

Fascinating article:

In the 1880s, Green said, turnout used to touch 80 percent. By the 1920s, it was down to 40 percent. The reason, he said, was a number of well-meaning electoral reforms.

Elections in the mid-19th century were festive affairs, and people gathered to carouse, jostle one another and vote. They sometimes cast their ballots on a stage to cheers and jeers. Voting, even their choice of candidates, used to be extremely public.

A series of progressive reforms in the late 19th century turned voting into a private affair. Campaign operatives were kept clear of polling stations. People got to vote in secret, and few knew whether their neighbors voted.

Turnout plummeted.

What this suggests is that, besides civic pride and political conviction, a central reason people vote is that democratic participation is an intensely social act. Politics, candidates and campaigns offer us zones of connection with other citizens -- even our political opponents. It gives millions of people common topics of conversation.

Voting used to be that way, too. We certainly don't want to go back to the time when casting ballots involved fistfights and booze, but the Michigan experiment suggests one way we can revive some of the social aspects of voting.
Your vote may count for very little in the outcome of an election, but it may count for a lot in the eyes of your friends and neighbors.

See the Washington Post article in full.