Can't enlist in black watch or wildling armies?

[Jamesol1]

I love starting off a campaign by choosing to enlist in the army of the house I plan to join/fight for. Both the black watch and the wildlings will be the first to fight the white walker invasion of which happens around turn 600 apparently but i can't enlist in any of their armies? When you join the Black Watch your only way to fight for them is to make your own army.

I know this isn't game breaking but I was hoping it would be something easily adjustable (unless there is a good reason as to why you aren't allowed to).

[H3YimDR3W]

I love starting off a campaign by choosing to enlist in the army of the house I plan to join/fight for. Both the black watch and the wildlings will be the first to fight the white walker invasion of which happens around turn 600 apparently but i can't enlist in any of their armies? When you join the Black Watch your only way to fight for them is to make your own army.

I know this isn't game breaking but I was hoping it would be something easily adjustable (unless there is a good reason as to why you aren't allowed to).

The reason you can't enlist with the nights watch is because you're either in for life or out. There's no enlisting then running away. You either join as a vassal and stay there forever or desert and risk everyone in the seven kingdoms hating you.