Since 1979, foreign manufacturing has grown massively at the expense of domestic, second, enormous advances in technology. Are you, presumably a software programmer, more productive because you're inherently smarter, or a harder worker, than a colleague from the 60s-70s? Or do you have much, much, much better tools, languages, frameworks, graphics, etc to do your job?
(You might even ask if you are, actually, more productive. Engineers in the 1960s created the 747 and put men on the moon. Not entirely sure either could be done today. GDP is not really the best way to measure "productivity.")