[Arryn]

Originally posted by Arralen:
Don't forget - there are still those build-in garrison archers manning the walls, or to be more precise, one or more towers only.

Which are inconsequential:

• They are still there, even after you breach the door and are allowed to storm the keep, so it's not like you must "knock out the pillbox first, so they stop resisting"
• They don't do enough damage to the type of attacker I sent in for that to be much of a concern.

I think the devs either don't want flyers to easily ransack empty castles, or they just overlooked the idea of the flyers-only attack. As such, a castle attack will always take at least 2 months, and thus risks the enemy having time to bring troops from nearby to relieve the siege. So much for the airborne blitz ...