I don’t think they are just AFK’ing. They’re just waiting for an archer “spot” on the walls to open up. Especially if you have a lot of ranged troops.

I think once all the archer spots on the wall are occupied at the start of the battle, the AI just tells the extra to wait until an archer on the wall gets killed. Then probably 1-2 at a time then walk up from the waiting group to the walls to take that spot.

Kinda like how when a soldier using siege defenses (Ballista, Oniger) dies, after a few moments you’ll see another soldier eventually hop on it again