Political scientists say that voters choose whether to vote based on the costs and benefits of voting. The higher the costs relative to the benefits, the less people will vote. Therefore, if voter turnout is low, it is because the costs are too high, the benefits are too low, or both.
Of course, voting does not literally cost money. However, there are still costs. One cost is the cost of becoming informed. In the US, we have many elections and it is hard to find out exactly what the differences between some candidates are. Becoming informed is a cost. Another cost is getting the time to vote. Voting in the US is done on a weekday, making it hard for some people who have to work to also vote. This is particularly true in places where there are long lines for voting. The time taken is another cost.
By contrast, there are few benefits to voting. The major benefit is a feeling that you have done your part either for the party you care about or for the country as a whole. However, these benefits are, in some people’s minds, being reduced by the dysfunction in our political system. If you are angry at both parties, it is not likely you will get a lot of satisfaction out of voting for one or the other.
Thus, there are a number of reasons why people do not vote in the US. They have to do with high costs of voting and low benefits.