Why? Because they were actual people with flaws and personalities? *Any* writing isn't made for you to "like" or not. Art isn't Facebook. Durance and Grieving Mother exist and are well-written regardless of my/your personal feelings towards them.
No, because they were one-note characters, that only muttered one phrase all the time. Durance was the godhating, rude, jerk of the group, who hated everyone and Grieving Mother is the overspaced, drugged person, who talks in flowery prose and uses some of Kreias tricks from Kotor 2.
If you combine them you would get Kreia, who was an actual complex person. You didn't like her, but she had some good points and you knew that she wanted only the best in her own, cynical, stubborn ways. And since the relationship between her and the Exile is something of an Mother/Child-Relationship, the Exile may also learned to love her or at least feeling at least pity for Kreia in her more vulnerable moments.
She was always Chris Avellones Masterpiece but Durance and Grieving Mothers are just a shadow of this and they get on your nerves, because you already know, that they will have a very dark secret and do some questionable thing and neither of them gets real character development. They are and always will be the group members nobody likes ... without the complexity of Kreia.
