Why does Miller keep giving Charley and Bernard scenes in this play if the play is primarily about the Loman family in Death of a Salesman?

The play is not really just about the Loman family, it is
about the contrast of a family whose ideals are unrealistic compared with a family
founded on hard work and realistic expectation.

Charley is
used as a contrast to Willy. Willy constantly criticises and belittles his friend, and
yet by the end of the play it is Charley who is providing Willy with an income. Willy
always resents Charley and never seems to accept that Charley is quietly successful,
while he is loudly unsuccessful.

Similarly, Bernard is a
contrast to Biff and Happy. He is mocked as the gawkish teenager, even by Willy, despite
his attempts to help Biff attain his dream of a place at the university of Virginia. It
is through Bernard that Willy pinpoints Biff’s demise, after he discovers Willy has been
unfaithful to Linda –

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BERNARD:…I’ve often thought of how strange it was
that I knew he’d given up his
life.

Bernard is quietly
successful like his father. He discusses how he is going off to do some work and play
tennis, when Charley explains that Bernard is arguing a case at the Supreme Court. The
brief but varied reactions in Willy show us how he is unable to understand the nature
and origins of Bernard’s success –

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WILLY [genuinely shocked, pained, and
happy]: No! The Supreme
Court!

Miller uses the
successes of Charley and Bernard to magnify the failures of Willy, Happy and
Biff.