Well, for one thing, the country seems to be very closely divided in politics, so neither the right nor the left is really getting what it wants. For another, many people think the system is controlled by big money and lobbyists. This last, though, may not really be true. For example, the Koch brothers have been talking about getting out of politics because they are getting so little return for what they have spent. They were especially angry that after spending so much to help the Republicans take over both the House and the Senate they couldn't even get rid of the Export/Import Bank.
Matt Yglesias summarizes the findings of a fat book by some political scientists that tried to analyze the impact of outside spending on the legislative process:
What Baumgartner et al. find is that across a broad range of issues, the public's fear that whichever side spends more will carry the day in Congress is misplaced. Resources spent statistically explain less than 5 percent of the variation in policy outcomes.The American political system is just set up to make it very hard to change anything, so if there is any controversy, the general outcome is that nothing happens. And this helps to explain this interesting finding:
But this holds for the boring and not-that-uplifting reason that the system embeds massive bias toward the status quo. Whichever side fights to not change things tends to win, regardless of who spent more money.
In a country whose politics are increasingly driven by principles-based ideological activists, a constitutional structure that makes it hard for anyone to prevail is a recipe for anger and frustration. A revealing 2015 Pew poll showed that Democrats feel their side is "losing" in politics by a 52-40 margin, while Republicans also feel their side is losing, by an even larger 79-14 margin.