The book Capitalism Hits the Fan: The Global Economic Meltdown and What to Do About It has the following explanation for political apathy:

The old and tired oscillations between “liberals” and “conservatives,” between Democrats and Republicans, remain the basis of mainstream US politics. Pendulum swings work now for Republicans, now for Democrats. What the swings leave unchallenged and unchanged is the class structure of the country – the capitalist arrangements of production that divide people and products into workers versus capitalists and wages versus profits. No significant political force connects this capitalist system of production to social problems. No such force advocates changing the class structure as part of a solution to those problems.

When class structures neither change nor even seem open to change, the endless political oscillations eventually convey their superficiality to the public. Politics then loses all contact with basic questions of choosing among alternative social structures and among alternative goals and strategies for social change. At best, politics interests specific sub-groups only if, when, and so long as some specific issue of immediate personal concern is at stake (abortion, gun control, gay marriage, oil prices, etc.). At worst – and the worst is what we increasingly experience – politics pits irrelevant tweedledums against tweediedees, cynically advertised candidate #1 vs public-relations-driven #2. People then turn away first from political activism, then from participation and information, and finally even from the passivity of mere voting. A mass alienation from politics altogether deepens, immune to the vapid exhortations to civic duty. Politics descends into a special branch of business where politicians make money and advance careers by mutually profitable relations with other businesses. This alienation – and the caricature politics it both reflects and enables – will remain unless and until a class-based politics emerges to contest for power.