Why are international institutions more popular than domestic institutions?

I am not aware of any survey that asks citizens to directly compare domestic and international institutions, but when people are asked how favorably they view an international institution, favorability ratings generally outstrip those of domestic institutions. This is true even in the United States. For example, a recent poll asked members of  the U.S. public the same question about six international organizations and  the U.S. Congress. The United Nations received the highest approval rating (60 percent) and the U.S. Congress the lowest. While there are clear partisan divides, support for the U.N. among Republicans is much higher than for any domestic institution.
Source: Pew Research Center http://www.pewglobal.org/2013/09/17/united-nations-retains-strong-global-image/
One simple explanation for this is that Congress is simply very unpopular (see here and here for the numbers). Moreover, the U.N. does not matter much to most Americans (although some want you to believe that the world body is about to take away guns, Mother’s Day and the entire American way of life). It is easier to like an institution in the abstract than one that interferes with your life in a more continuous way.
This is not so in Europe, where the European Union clearly affects the lives of citizens. Yet, even amid the current crisis, the E.U. is still trusted more on average than national governments and parliaments (see graph below).

The graph below shows that in two-thirds of the 27 E.U. member countries, trust in the bloc exceeded trust in national governments in 2013 (these are the countries above the diagonal). This is lower than in the years before the crisis but still considerable. The finding also holds for other institutions. For example, I showed in other research that trust in the European Court of Justice tends to exceed trust in national judiciaries. Clearly, there are exceptions, but more often than not the data I have seen support the idea that publics in most countries are on average at least as supportive of international institutions as they are of domestic institutions — in some cases more supportive.

Why is this so? After all, governments rarely shy away from blaming all bad things on international institutions. Moreover, we are constantly told that citizens do not like it when foreigners with questionable accountability can influence their lives.
There are several plausible theories. First, it may be related to performance. As Daniel Drezner puts it,  the “system of global economic governance has worked,” given what it was up against. By contrast, many domestic governments did not do so well, although there is variation. It may not be a surprise that Germany (DE) is below the line and Greece (EL) is not. Indeed, many countries above the line are places where national governments are trusted very little and the E.U. does only marginally better.
Another functionalist theory is that international organizations help citizens make sense of interdependence.  For example, there is good evidence that U.S. citizens view the presence or absence of U.N. authorization as a “second opinion” on whether a proposed use of military force is a wise idea. Citizens may suspect that their own government has incentives to misrepresent motives for military action or else they simply are not sure what the consequences of a proposed military adventure are likely to be. If other states who generally do not agree with the United States approve of an intervention, then that serves as a powerful signal that a use of force may be worth it. There are other informational or credibility theories along these lines for different types of institutions. The general implication of such theories is that the higher levels of trust do not mean that citizens would like their domestic institutions to be replaced by international ones but that the multilayered system has value, in their view, given that we live in an interdependent world.
A third hypothesis is that international organizations are perceived as less partisan than are domestic institutions. After a polarized election, a sizable minority of a country may not trust a specific government, even though they still value the domestic  system of governance. This may not be so at the international level, where the partisan composition of institutions is less fluid and less visible (although support for international institutions is generally correlated with partisanship, as the U.S. figure above shows).
Fourth, people may be much more cosmopolitan than generally believed. People may, for example, have started to form true European identities that drive their support for and opposition to European institutions. Similarly, research shows that attitudes toward trade and outsourcing may be shaped more by attitudes toward foreigners and foreign countries than by economic rationales. Education is often key to this argument: As people become more educated they become much more cosmopolitan in their policy attitudes.
These views are not mutually exclusive, so they could all contribute in some way. There are surely other ways to think about the matter, including that these poll numbers merely reflect poor information about international institutions. Anyway, it strikes me as an interesting puzzle that could use some more research (or there may be research out there that I am not aware of and that gives a better answer than I have given here).