Norscan Legendary Lords quickly confederated the Norscan continent using their racial confederation. This removes the ability to gift a homeland region to those confederated factions, unlike when they are destroyed. Tong, a minor Norscan faction does not exist at the start of the game and can be gained by taking a settlement in their homeland and selecting the gift to vassal option.
Bellow are images of an example.
Taking a settlement before taking the bound fortress.
Taking a settlement after taking the bound fortress.
This issue severely restricts the number of possible vassals a WoC faction can have and it is unavoidable since many confederations happen before it is possible to reach the major norscan factions to prevent the confederation. Even if it is not a bug, the factions that have a homeland should always be available to resurrect as WoC.