Do bandits mint their own coins?
They have coins as treasure, right? So they must be minting their own currency.
Savage humanoids -- goblins, hobgoblins, gnolls, bugbears -- have gold, too. And steel weapons. Even though there's no reference to them even knowing how to forge metal, or having much technology of any sort. The JG Ready Ref Sheets list them as "semi-intelligent", not even as advanced as cave men. But they have all this man-made stuff. How did they get it?
It's been popular for decades to say that D&D is about "killing monsters and taking their stuff". It's a joke, but some people take it more seriously and complain about the immorality implicit in D&D. The latest snide bit of jargon is "murder hobos". Those adventurers, they are so terrible, breaking into someone's home, killing them, and taking their treasure!
But where are these creatures living? Usually in the remains of some human construction that was taken or destroyed by an invading horde. Where did they get that gold? If not from robbing travelers, they probably looted that "huge, ruined pile".
What I'm getting at is: the original game proposed reclaiming lost treasure, either taken by savage invaders and bandits or left alone in ruins prowled by murderous beasts, magically-created menaces, and the angry undead. If you change this to fully realized goblin cultures and then propose that the PCs should kill and rob the goblins of what's rightfully theirs... well, that's not a moral failing of the game.