The whole saga is based on the powers of Ender in dealing with relationships, influencing people to better them and how much of an impact Ender has on people(supreme commander and all).
That's the thing that makes him the best commander of humankind, and throughout the book he has changed the lives of a lot of people and that is indeed shown in Speaker for the Dead.
When he came he stirred things up pretty fast and made a huge impact in that community and with Novinha's family. But then he stays and marries her, and flash forward to the future and Grego and Quara are still kind of dicks and Ela too sometimes.
Novinha certainly is still a very cold broken woman, and although Quim and Ender have a relationship of mutual respect it's still not great. The one that he has had an impact is Miro of course and Olhado.
But in general they are still a fractured and disfunctional family, so how come people's lives are greatly changed by just a few moments with Ender, but a family with a lot of years (even a lifetime) of living with him are still basically the same?