Most of Willie's memories are from 1928. Why does Willy's memory return to 1928? Why is the contrast between 1928 and the present significant for Willy and for the play as a whole?

I dont know someone answer please???

In 1928, Willy averages the highest monthly salary with his boss, Wagner and when Willy approaches Horald Wagner, Wagner's son, he didn't accept Willy on his company because he is to old. With this case, Willy told this matter to Harold.