@Mojo
Well put it this way... suddenly 2 ppl approach you... only for them to tell you, hey, guess what, I am your husband's OTHER WOMAN and this girl is OUR daughter and we're here to stay at your place and free load.
That won't go down well with you would it
Yea polygamy is accepted, but women vie for the "lady of the house" role. If they introduce themselves as widow/cousin, then they would eliminate themselves as a potential threat to the Lady of the house.