It's long been a frustration of mine how guys in America seem to often try and "get away with" the most casual thing they can wear anywhere. I saw this quote from this article on PutThisOn a couple days ago, then recently came across the full interview. Definitely worth the read:
Some Personal Thoughts
While I find the article really interesting and agree on a lot of points, I don't think her conclusions tell the whole story behind casual wear attitudes in the US. Casual wear encompasses many more styles and genres as opposed to getting "dressed up," which generally still means a dress shirt and/or suit (though I would point out that wearing a suit or more formal attire still affords a great deal of individuality and personal expression - just look at the Italians). So in terms of the numbers, the math simply favors casual wear for having the most amount of styles and silhouettes as a means of expression. But as much as I want to think the casual attitude of American dressing is rooted in a greater freedom of self-expression, I don't think that's it.
A lot of guys get overwhelmed when trying to buy a suit, dress shirt, etc. because they don't know what they're looking for, and often many things can go wrong when starting out. At the end of the day, for many men it's a lot easier just to throw on the ol' cargo shorts and a T shirt than taking on the task of learning an entirely new way of dressing. I think this is the major reason behind the casual culture of Americans. It has nothing to do with style or expression.
Fortunately, the past decade has seen a lot more men really start to take an interest in the clothes they wear. With streetwear really hitting its stride, it very well could lead towards more casual trends in menswear, but hopefully for all the right reasons.