Laziness, ignorance, apathy? Who knows, but I always kind of chuckle when people complain about their politicians but don't vote and don't really know much about them. I agree it sucks sometimes what choices are available, but there usually are ballot issues and there usually are third party candidates one could support in the hopes that it will encourage breaking the two-party stranglehold.
Here we just had a primary last week. Took about 10 minutes out of my day to go vote. Total turnout was about 15% of eligible voters. One issue, a library millage, passed 2,300 to 2,100. It is pretty amazing to think that 200 votes is all it took and I started thinking about how if anyone could patch together just 2,000 votes or so, you could get anything passed.
Democracy can't survive without informed, engaged citizens. We are proving that to be true.