The answer, of course, is that Congress is unpopular. However, just because everyone hates Congress, that doesn't mean that Congress is to blame for everything.
I'm responding here to a post by Matthew O'Brien, who reports that economists blame Congress for failing to do two obvious (to the economists, that is) things: tax reform, and infrastructure spending.
I'm okay with blaming "Congress" for not passing tax reform. The problem with tax reform is that (1) it tends to give generalized benefits and particularized costs, and (2) it's rarely at the top of either party's priority list. I do think that it's possible we'll get tax reform should the elections return divided government, and I'd probably blame democracy in general rather than Congress in particular, but I have no problem with an assertion that the structure of the US Congress tends to make the general democratic preference for avoiding policies with specific, visible costs even worse.
But infrastructure? No way. The infrastructure problem isn't the fault of Congress; it's all about the Republican Party. You get a landslide win for the party that wants to slash government spending, and you're going to have less spending. Especially if that party wants to slash spending but also ran against Medicare cuts, opposes Social Security cuts to current recipients, and supports increasing military spending. So blame the GOP, or even blame voters (although I wouldn't; they didn't have a specific choice about roads and bridges and the rest), but don't blame Congress.
The general rule about all these things is that it's a lot easier to blame either something that everyone hates (Congress) or something high visibility (the president) than it is to actually figure out who is responsible. But if you either just want to understand what's going on or especially if you want to affect public policy, you're far better off if you do the hard work of figuring out exactly who does what and why.