One (of many) features I like about Beedo's new Black City campaign is the presence of other adventuring parties. They set up camp, they raid areas, they raid each other, etc. Competition.
My current game doesn't have them.
The simple answer is, it's a "dry hole."
As far as the locals are concerned, the dungeons up on the mountain are pretty much devoid of anything useful. The only things up their are fierce monsters, dangerous vermin, old traps, and treacherous grounds. Local legend puts nasty, nasty stuff buried up there, or nasty, nasty stuff long dead and looted. Local hunters know it's dangerous.
The occasional people do go up and explore, and most either come back empty handed or with a bare few coins or salable bits of junk. Others never returned - either dead in the ruins or they head out, too ashamed (or poor!) to come back to town.
The PCs have proven this to the locals. They've made three trips, and came back fairly battered and/or exhausted each time, with a bare scraping of loot that didn't even pay for expended arrows and used-up supplies. They keep expending cash on necessaries, but can't afford to celebrate or upgrade their gear. As the locals see it, they're digging in a dry hole and doubling and tripling down on a bad decision.
The local economy "senses" this, too - alchemists will make a few extra healing potions, sure, but won't go all-out supplying adventuring goods. Local weapon makers won't try to stockpile arrows and thrown weapons. Items will need to be special ordered and not found off-the-shelf.
This will change once the PCs make their first big score, locals will notice. More "adventurer" type goods will show up as people speculate on the demand. Maps someone's brother's sister's cousin drew up will get found and dusted off and offered for sale. Some of the braver types might take a trip up there, even, and see what they find.
Word will start to spread, unavoidably - unless the PCs choose to avoid the city, and not spend any money at all there, which means willfully forgoing the benefits of their loot. The more loot that comes, the farther and faster the word will spread. Outsiders will start to show up. NPCs will start to organize groups and go on. Competition will start up. Local notables will get involved. How the law will react is as-yet unknown. Will murdering fellow explorers in town be illegal, but what happens underground stays underground? Who knows?
But once the money starts to flow, the local economy will transform and speculators will start to swarm in. It'll change from "sleepy Stericksburg" to "Stericksburg, City of Adventure!" in no time.
But it hasn't done so yet. It's still a dry hole.
This opens up the question, "Why do the PCs keep going?" Out of game, it's simple - I told them that the campaign focus is that dungeon, and my players are happy to go where the game is. In game, we explained it like this - Vryce (the knight and highest point guy) is convinced, firmly and deeply, that the rumors he heard about "more and better loot" being down there are true. He won't give up and go home till he finds it. When they do, it's going to change the nature of things. For now, the PCs are the only fools willing to die for coppers . . . as the locals see it, that is.