As WW2 was ending and the war production machine coming to a grinding halt it was assumed that the US would revert back to Depression days, particularly with so many young men returning from battle. In fact, there was an initial slowdown and people professing that we would soon be back to soup kitchens and men selling apples by the side of the road.
That did not happen, and for a number of reasons. First, the GI bill was used in part to defer young men from going into the workforce. My father used the GI bill to obtain an engineering degree based upon interests he developed in the Army. He was the only sibling out of 13 to secure a college degree. Also to the point, men received training in the war they would have never gotten on their own. The first commercial jet pilots in the 1950s were mostly WW2 air core.
Second, was the pent up demand and need to replace durable goods. From 1942 to 1945 you couldn't buy a new car, fridge, stove, etc. The television was introduced in 1947. Soon factories were humming with demand for new Fords and this new medium, television. Back then durable goods had a far shorter life span. The velocity of money takes over as factory workers flushed with cash could no buy or desire and want, not just absolute need.
Third, until the entrance of Japan in the early 1970s all other countries had little or no industrial base. Moreover, technology that was based upon large onsite mainframes meant offshoring production was impossible. The introduction of the desktop in the 1970s changed that scenario, along with more modern and regular air travel. Countries opening their economies also was instrumental.
Fourth, more workers were covered by unions and unions had more sway. They could cripple a company's operations through a strike (and many strikes took place). Eventually after the two sides had enough financial pain they found a compromise.
Fifth, we were fighting a massive campaign with the Cold War. The US was out to prove that capitalism was far better than a planned, central economy. That would not have been possible if jobs were moving overseas and vast underemployed ran wild.
Sixth, with the Depression fresh in the minds of American and politicians, and no politician wanted a repeat of the 1930s, economic and Fed policy was dedicated towards full employment. By the 1970s 20 years of full employment, ever rising wages, and misguided policy was causing double digit inflation. Finally by 1980 Fed Chairman Paul Vocker did something unthinkable; he jacked up interest rates to unheard of levels even though it caused a deep recession and high unemployment (that at one point reached low double digits). From then on the focus of the Fed and the Treasury was the control of inflation versus super low unemployment. By 2008 monetary policy no longer worked to juice up the economy, although that did not stop the Fed from using it.
Seventh, was the significant amount of personal and corporate savings and low levels of debt. Prior to the 1970s most Americans did not have a credit card, or maybe something like a department store card. Starting in the 1980s bankers threw out financial prudence allowing Americans to load up on debt to enhance their lifestyle. Moreover, the introduction of securitization in the 1970s meant that banks would no longer hold those loans on their balance sheet. They simply sold off the loans, collected a nice fee and re-lent, repeating the process over and over. However, with the risk off their balance sheet credit standards quickly eroded. The end result is that there is far fewer dollars for productive investment. Companies have loaded up on debt to do acquisitions (which destroys employment) and stock buy backs (which adds nothing to employment).
This is not an exhaustive list by any means. That period was a conflux of circumstances, policy, global position, changing culture and morals, military might, management focus, etc. This is why its so difficult to return the US to its glory days of 1946-1980. Yes its possible but many parties would want this to occur, and two the major participants, business and government are not ready and willing to change. Not to mention Americans would have to give up their love of cheap crap from China and save instead of consume.