In August Wilson's play Ma Rainey's Black Bottom, why are various characters given unusual names, including nicknames?

Nicknames are used in August Wilson’s play Ma
Rainey’s Black Bottom for a number of possible reasons, including the
following:

• to contribute to the play’s informal,
  colloquial tone


• to help distinguish Ma and her band from
  the more conventionally named characters of the play


• to
  help imply the relaxed familiarity of the members of the
  band


• to make the informal names of the band members seem
  appropriate to the kind of informal language they speak. At one point, for instance,
  this exchange occurs between Irvin (a white man) and Cutler (an African
  American):

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IRVIN  Where’s . . . uh . . . the horn player . .
.  is he coming with Ma?

CUTLER  Levee’s supposed to be
here same as we is. I reckon he’ll be here in a minute.  I can’t rightly
say.

Cutler’s language is
more colloquial, more regional, and more distinctive than
Irvin’s.

• to make the band members seem
  unpretentious and thus more appealing and more accessible to the
  audience


• to help distinguish the African-American
  characters from the whites.

Thus, the white
characters Irvin and Mel Sturdyvant have names that are far less intriguing and
suggestive than those of some of the black characters.  Many of the black characters are
given names that make them seem more interesting and exotic than the white characters –
as if their names have been “earned” rather than merely affixed at
birth.