so first off, they would never EVER even consider just leaving all those armors and weapons on the battlefield like that, far to valuable, secondly, captured enemy soldiers is a valuable commodity to be held for a ransom, and it would also be fairly easy to squeeze them on information as well.
the tendency mangas set in medieval like eras has to just leave highly valuable armor just lying around like that to rot is one of my pet peeves, why the hell would you do that? bring as much of it with you as you can, and if not to far away it may be worth it to hide what you cant carry to come back for it later.
in this chapter it is just outside their own castle gates, take everything, fix what can be fixed and use it, recycle the rest.