They need new people who have no affiliation to the cast. That's what made Kenya and a Porsha food additions. No one new them and they started friendships and conflicts on their own.
Usually, they add people who are loyal to a person on the cast . Eva knew Nene and said she was warned about Cynthia and Kenya early on, so she didn't like them. Shamea is up Porsha's butt. Yovanna just proved she can be manipulated for a peach. Tanya has already been tainted, as was Marlo.
New blood needs to be NEW.