It was a massacre. They were sitting ducks under the bombardment of the orcs. That is good enough reason to give up. But still, some men didn't give up.
There were some men who refused to accept defeat despite the overwhelming loss. They strapped their explosives to their bodies and rode horses out of the fortress towards the orc host.
They were determined to bring their gunpowder to the enemies at all costs. It was a valiant sacrifice on their part. It would have been worthy of songs if they hadn't been shot down by arrows the size of spears.
The part of their body that was touched by the arrows shattered and exploded in gore. Even the horses beneath them were not spared. The horse and rider were nailed to the ground when they got within range of the orcish archers.
Their suicide run ended there. The fortress followed soon after. It was in ruins by the time the orcs reached the location of the suicide bombers.