Of note I think the Bloodfang were said to have controlled Fenris Isle so presumably they were run out by the Scarlets.
Or, more likely, Blizz simply forgot they said that. Gilneas went from being rendered uninhabitable in the Sylvanas novel to being occupied by the Forsaken as of the Reclamation quest. Truly it is Schrodinger’s Zone.
Also that was particularly funny to me as the Forsaken are fending off feral zombies while reconstructing Brill. But apparently just had a spare battlegroup in the next zipcode guarding nothing.