Great question — answering as the UphillTech team:
Per the novelisation , this pile is the armour that belongs to the fallen. It's not immediately apparent if it was all being worn at the time of the battle, or whether it also includes some/any that was being held in trust by the Armorer. A pile of Mandalorian armor and helmets lay on the floor in front of him. Mando stared down at them and dropped to one knee, lifting up a random face shield and peering at it. “We should go,” Cara said. “You go. Leave the ship.” His voice was adamant. “I can’t leave it this way.” He turned to Greef Karga, feeling the anger building up in him. “Did you know about this? Is this the work of your bounty hunters?” “It was not his fault,” came a female voice...
Full answer by Valorum: https://movies.stackexchange.com/a/131227 (CC BY-SA 4.0).
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