Imagine Bretonia claims a planet so CR officially gives them that planet to shut their mouth and Bretonia turns back most of its attention to their Omega efforts. In the meanwhile the rest of the Tau factions, CR, IMG, NO, Zoners, slowly migrate to and populate the planet (as much as a barely terraformed planet can be populated), and eventually Bretonia ends up having military/police control and authority over a culturally foreign planet. Once they start to care about Harris more, what do you think how long they can hold and do anything they want with it? Mind that iirc it doesn't have as much BAF forces watching over it as GranCan does.