Gallic Junkers are being intimidated by the Outcasts and are forced to cooperate with them.
This is how the Outcasts got their base in Lorraine- Bribing them. Those they couldn't bribe? Threats and intimidation until they cooperated.
As for La Brise, we're attempting to stop the Cardamine trade as it is an outside influence which profits to another group than the Corse itself. In the case of artifacts, we gain the largest part of the pie within Gallia. Outcast policies on Cardamine would actually lessen the Corse's influence and harm their actually strenious relationship with the Royals, and lessen any trust the Council may have towards them. The Corse may not like anybody, but they need to be in good stance with as many people as they can to live.
There actually is a Corse-Council anti-Outcast alliance, as well.