They did. My dad raised a family, helped send two kids to college, lived a solid middle-class life, and retired with a pension on a high school degree and a career at the Ford plant. He's not alone. Manufacturing and construction provided middle-class lifestyles for millions of people in this country. But now manufacturing is chasing the cheapest wage overseas and construction has been populated by foreign workers willing to work for a fraction of a U.S. worker will.
The fact is, the key is now and has always been "value-added," and menial jobs relatively speaking add very, very little value.
Amazing how you concluded that working in manufacturing is menial and adds little value. What do you think creates the product from the pieces? Pixies? U.S. factories consistently out-perform foreign workers in terms of quality and productivity. You don't do that with a dumb workforce. But corporations still look for the cheapest salary rate.
And designers, inventors, innovators are not pixies. They are the ones who add the value. It should tell you something that these jobs can be performed by incredibly low-skilled people overseas. If they were as value added as you say, only a handful could do them. It is precisely because these jobs add little value overall that they can be outsourced.
BTW, you seem to be making a case for college by citing a "dumb workforce." In fact, American workforce is getting much more educated---as it always has been throughout our history. US skilled workers have always outpaced other countries because of availablility of land and ability to start your own business.