Voting in the US matters less than most developed nations, for one very important reason: We vote for too many offices. While this may seem like it makes your vote matter more, it actually makes it matter less, because it is practically infeasible for enough people to inform themselves about the massive number of candidates and positions that we have on the ballot, so the vast majority of the votes are guesses at worst, party line choices at best. In countries the elect fewer positions, the people you actually do elect appoint those other positions, making the vote for that person both individually more important, and substantially easier for the average person to have a reasonable grasp on.
TL;DR: Your vote isn't that important when massive numbers of voters aren't even educated on the very, very basics of most of the candidates and offices on the ballot. It waters down the vote.