I mean, on the one hand, manufacturing has grown near-continually for those 70 years, and its demand for labor has reduced. So, it's not like you're wrong.

At the same time, our production of lower value, commodity-ish things has indeed shrunk rather than grown with population of demand. That manufacturing expertise is more concentrated more on higher value (aerospace, information technology, etc) things and less on fasteners, bulk materials, or extrusions.

We are not vertically integrated in the way that China is.