"Hrmm, a masterwork greatsword made out of adamantium costs 3,200 golds. A full suit of plate armor made out of adamantium costs 50,000golds."
"Hey wait, training a new claymore only costs 200 golds. Plus we can recycle the swords, so long as the soldiers don't see us grab their grave markers."
"Endless cannon fodder girl soldiers? BRILLIANT."
It's kind of like why 17th-18th century armies didn't equip their soldiers with breastplates, greves and helmets. Cheaper to just hire a new soldier.