There's simply no ROI for this. You're talking about 3.6 million unmotivated teenagers yearly who need to be transported, housed, and fed just for them to dick around for a year before moving on to their actual goals. As for national service being mandatory for citizenship, that flies in the face of the very reason we fought for our independence. National service via the free market and free will is no less "American" that going into the military, there is much more to our culture than warfare or even government service.