I did vote so this isn't my personal opinion. I've been told many times it's "voting for the lesser of two evils, they're both evil and I don't agree with either." There's no real sense of choice. I can see it. It very much feels like that South Park episode where they have to vote for the school mascot. Do you want it to be a Giant Douche or, a Turd Sandwich? And then at the end it was all for nothing because they don't change their mascot so it was all pointless.
Edit: you guys can call me stupid all you want. It doesn't change the fact that I've heard this from coworkers and family repeatedly. I did vote. In fact, I've already voted in my primaries. The question was "why don't people vote?" I gave the answer of why I personally have been told by people they don't vote. Not liking my answer doesn't change the reality of it. I work in blue collar work. It's a very common view in my area. Or, they are pro Trump.
My personal opinion on why they don't vote or, don't vote in favor of things they support, they generally don't want to take the time to educate themselves. And for others, they don't want to feel responsible for voting when their candidate turns out to be nothing like they promised.