Mostly because government stayed the hell out of the way

During 1946, civilian employment approached 58 million. This was the highest civilian employment this Nation has ever known— 10 million more than in 1940 and several million higher than the wartime peak. If we include the military services, total employment exceeded 60 million. Unemployment, on the other hand, remained low throughout the year. At the present time it is estimated at about 2 million actively seeking work. This is probably close to the mini- mum unavoidable in a free economy of great mobility such as ours.

Thus, at the end of 1946, less than a year and a half after VJ-day, more than 10 million demobilized veterans and other millions of war- time workers have found employment in the swiftest and most gigantic change-over that any nation has ever made from war to peace.