In a society of war and struggle, there is no place for the physically weak. Goblin society is especially harsh, as the Goblins have spent hundreds of years losing wars to the good beings such as the Elves, Halflings and Dwarves; and being betrayed and enslaved by the Orcs and Dark Elves.
In a desperate attempt to utilize all members of Goblin society in the war effort, those Goblins found not fit for regular combat are given large bombs to deliver to their foes' armies or city walls. Though no Goblin volunteers for the job, Bombers are heralded as true heroes.