You'll notice that while the United States is near the bottom for percentage of voting-age population (the blue dot), its percentage of registered voters (the tan dot) is very high, 84.3 percent, which is up there with the top five countries on the list. What that tells us is that even though nearly half of Americans could potentially vote don't, at least most Americans who bother to register to vote end up doing it. USA! (?) USA! (?)
As Pew noted, that's because voting in the United States is "mainly an individual responsibility." In most states, residents have to go out of their way to register and vote, so the pool of "registered voters" is a self-selecting group. Of course, they're more likely to vote because they made the effort to register in the first place.
That won't be the case in Oregon when voters there head to the ballot box next. The state passed a bill in March that will automatically register anyone who's had an interaction with the DMV since 2013, so it could be a test case of how much increasing registered voters leads to increased turnout. Other states (including Oregon) are also embracing vote-by-mail systems, which increase turnout.
But if the United States really wants to boost turnout numbers, it could always make voting mandatory. It's worked well for turnout figures in other countries such as Belgium (No. 1 on the list), Turkey (No. 2) and Australia (No. 5). Other OECD countries with compulsory voting are Greece (No. 12), Mexico (No. 18), and Luxembourg (No. 26), while France (No. 13) has compulsory voting for its Senate races only, according to the International Institute for Democracy and Electoral Assistance.