That's the heart of the matter. The major parties have a virtual monopoly; we're as trapped as voters as consumers are in a market monopoly.
I think the way we fix this is weaken the monopoly of the major parties, possibly with things like ranked voting: http://www.fairvote.org/
Which Maine is trying to institute: https://ballotpedia.org/Maine_Ranked_Choice_Voting_Initiativ...
Perhaps we should try to institute laws that break up parties if they get too big the same way we can break up corporations that are too big? Monopolies being bad an all.
I don't think the ~15% of people who are at poverty level care as much about privacy as they do about getting a better job or getting proper healthcare, for example. You'd have to form a pretty strong voting bloc just to offset those votes.
You vote 3rd party for someone who is and bitch at whichever major candidate wins regardless (which is why they resort to form letters, so at this point its newspaper outlets/townhalls/etc).
Democracy doesn't end at the voting booth and you have to put continual, sustained effort to create change. Look at the GOP running and hiding from their townhalls over Healthcare. Imagine if that was for privacy-related issues (or whatever). Sure, it may not work with the GOP but the Democrats might seriously consider adopting it to try to split voters away from the GOP.
There are a number of pro-privacy representatives, and one or two senators, so it is not like people aren't votinig at all, but if you don't get a choice then you cannot be blamed for failing to make the choice.