The play Death of a Salesman by Arthur Miller is set during the end of World War too, circa 1945. This is a period that preceded the booming 50's. This was a time of improvement in financial and technological areas because after the war ended, new doors and policies allowed for more chances to earn a living. This is also the period when America became the bona-fide "Superpower of the World".
The comfort of secure jobs and a growing economy allowed people to trust get-rich-quick schemes that closely followed, as they often do in times where people are willing to take chances to improve their status. The use of credit cards was rife at the time, because people were learning this method of buying now-paying later. It was easy for them because, after all, they always had the money to pay. However, when the comfort zone became more and more tempting, credit lines began to override cash purchases and people began getting into debt. This is the case of Willy Loman.
Ironically, Miller emphasizes the do-nothing aspect of Willy's sons by assigning them the two jobs that were most affected during this economic growth: The farm industry and the unskilled labor industry. Biff and Happy each belonged to those fields. This tells us that the Lomans were indeed going all the way down when things turn around.
Hence, although the play is based in a period of economic prosperity, the Lomans chose the wrong dreams to follow, and could never find what they really wanted.