I think the two party system is ultimately to blame for this, though I have no idea what the solution would be. Up in Canada, we have three left-leaning parties, NDP, Liberal, and Green, which represent some very different political views but all have varying levels of representation in our parliament.
After living in the States a few years it's become clear that none of the 3rd parties are taken very seriously, and if you're not R you've gotta be D, and vice versa. For a country where I've met so many sharp and politically sophisticated folks, I think it's a bummer they have one binary choice when it comes to their national vote.