In "Death of a Salesman", why don't Biff and Happy get married and/or settle down?
Biff and Happy simply are not equipped with the things they need to get married and have a successful marriage. We can point to their parents for reasons why.
Willy has had an affair and Biff and Happy have grown up knowing that their parents did not have a happy marriage, although it might have appeared they did as on outsider looking in.The marriage was superficial because they both lived in a dream-world, one of appearance, not reality. They both wanted their dreams to be their reality so badly that they avoided addressing the real problems in their lives. Biff and Happy have learned this from their parents; therefore, they are not equipped with the reality and/or emotional tools they need to get married and have a successful marriage.