Don't forget that Junkers do smuggle both Artifacts and Cardamine illegally through GMG space, and doing so at their own risk. It's not uncommon that a few Junkers will try to break free with force when cornered with contraband in their holds.
But if the Junkers start misbehaving and harassing GMG ships, you can wave Yanagi a good bye.
The GMG recognize the Junkers' practicality, but do not depend on them. Dirty garbage rats still have their uses, even so.