Subject: Why are astrophysicists looking for only one source of dark matter?

Every article, book or TV program I have read or seen about the search for "dark matter"  casts the question in terms of the search for one single source of this "missing" stuff in the universe.  Whether the particular astrophysicist/astonomer/cosmologist involved is looking at MACHO's, WIMP's, brown dwarfs, neutrinos or something else, they talk in terms of "the" source of the dark matter.  Are there important theoretical differences that would separate a MACHO-dominated universe from a neutrino-dominated one?  Or is this more a result of human nature, i.e., each investigator has his or her own personal favorite that they are trying to establish?  Couldn't the dark matter be a sum of many different things?

Re: Why are astrophysicists looking for only one source of dark matter?