Why is Greygore Boomhowler a merc to trolls. No one else can use him other than trolls. He is Admiral Boomhowlers brother… I know lore does not drive rules.
Just makes a combat solo less attractive when my feat, spells do not interact with him etc…
All MK IV mercenaries so far have worked for at least two different armies.
He probably works for another (unannounced) army.
He’s always been a Mercenary, just in this case he’s out before the other Army that can take him. We know from his retailer solicitation that he works for Brinebloods and “an unannounced Army”, so we’re just waiting to find out what that is.
Story in universe reason is what your asking?
Siblings man. Do they ever take to one being in charge of the other? Big personalities like the Boomies just clash normally but these two have a whole sibling rivalry going on. Does Greygore like the idea of having to come to his sister for work these days? No not really. Is he getting a lot of work outside them at the moment. No not really. His sister is very smug about this.
The rules reflecting this is very intentional
Without spoiling too much from the app subscription, Admiral Boomhowler’s “Heros & Villains” article does a good job of explaining why Greygore became a merc in the first place