Why can;t you form Austria as Tyrol or Salzburg?

[unmerged(271387)]

Since both are Austrian and can't form Germany,and by looking at the decision files it seems only Styria can form Austria.I would like to know why this happens.

 

[Sleight of Hand]

Salzburg is a bishopric and so that wouldn't be right, but the other Austrian duchies make sense, yeah.

 

[Doukan]

Because this is Austria, and this is Tyrol, they are both minor regions (one of which become very prominent).