why unspecified is captured in marketing channel processing rules

Hi @prakashr,
A lot of these answers can be found in the online reference material:
https://experienceleague.adobe.com/docs/analytics/technotes/unspecified.html?lang=en 

The reason Unspecified appears is because any data that has not been specifically identified by the Marketing Channel Processing Rules gets lumped into this bucket.  The same goes for Classification Rules as well.