Why are us USA citizens so patriotic whereas other countries are more casual and understanding that their countries have issues?

 Freedom. Freedom to prance around and hold our heads high. If you can't do that, you have no idea what freedom is all about. 

I have the freedom to dress in a bright pink leotard and walk down the street signing show tunes. The fact I have the freedom to do so does not obviate the fact I'll look like an idiot if I do.

  Uh, please don't wear the Batman suit as shown above.

My not-very-scientific hypothesis is America, being a country of immigrants, largely lacks the deep cultural roots which other countries/cultures have. Hence, we are not unified by our common history, common language, common religion, common cultural practices, and so forth. All we really have is our political identity as 'Muricans. What else have we got to play up and be proud about?

I suspect overlaying that sense of cultural rootlessness is the understanding (even if subconcious) that given how powerful and wealthy America is, it has done a comparatively s***ty job of being a "good citizen" nation-state, as pointed out by Aaron Sorkin.

So, in order to resolve the cognitive dissonance, many Americans resort to turning up the jingoism knob to 11.

Because they swallow that whole 'American exceptionalism' thing , much like their best buddies Israel do.

I think Americans are just more gaudy about it, if that makes any sense. I know a lot of other people who are just as passionate about their countries as I am about America, but they don't feel the need for showy displays of patriotism. It's just something that comes out in their thoughts, actions, and what's in their heart. 

Because AMERIKA!

Patriotism is a tool.

Authorities like to cultivate a sense of identity and belonging in order to help teams pull together for a common goal.

This works in sports, big business and war.

I do think Americans are more "out there" and expressive than many other nations.

Simply incorrect.   Other countries make a HUGE deal out of celebrating their country, patriotism, heritage etc.  All of them do.  Even Ethiopia and they don't even have food.

Of course, of course. Obviously of course.