Why does Willy tell Howard about Dave Singleman in Death of a Salesman?

Let us remember that at this stage in the interview Willy
senses that things are going badly for him and he is fighting for his job. As he tries
to engage a "barely interested" Howard in what he is saying, he reveals his own
inspiration and role model for becoming a salesman, who was Dave Singleman. Note what he
tells Howard about this legendary figure (to Willy at
least):

And
he was eighty-four years old, and he'd drummed merchandise in thirty-one states. And old
Dave, he'd go up to his room 'understand, put on his green velvet slippers--I'll never
forget--and pick up his phone and call the buyers, and without ever leaving his room, at
the age of eighty-four, he made his living. And when I saw that, I realised that selling
was the greatest career a man could
want.

Of course, it is Dave
Singleman who gives the play its title, as it was his death that brought "hundreds of
salesman and buyers" to his funeral and made things "sad on a lotta trains for months
after that." Dave Singleman thus represents the personal side of sales, which is in
direct contrast to the impersonal reality of sales that Willy is confronting now. In his
own words to Howard, it is "all cut and dried" and there is no room for "friendship." Of
course, the massive irony of Dave Singleman is that Willy's "death of a salesman" is
completely different to Dave's. Willy dies unremembered, apart from his family, and
represents a victim of the capitalist system rather than a hero.