I'll quote my response to Alexis and his response to me in full:
Why do the monsters build so many traps in the dungeons?
My question is actually, do monsters build the traps?
In the real world, where are traps encountered? Tombs such as the Egyptian pyramids and other pharaonic tombs sometimes had them. The tomb of Chinese emperor Qin (where the terra cotta army is) is suspected to have more treasures in it protected by traps. These days, though, we don't usually bury people with grave goods, so there's not much need for traps.
We do have other sorts of traps, though. Modern security systems include alarms and cameras (which are trap adjacent) and things like auto-locking doors or gates that close upon an alarm being triggered (which I would consider as actual traps). But these sorts of traps aren't everywhere. You see them in banks, high end jewelry stores, wealthy peoples' houses, and other places where there are things of value. Cameras and alarms have become much more common, though. Electrified fencing could also be seen as a form of trap, I suppose, keeping people out of (or in) a certain area.
Also, in war, we use land mines, and sometimes guerilla forces use things like tiger traps (think Viet Cong) or the like. In general, we have decided that people don't deserve to be peppered with poison darts or threatened with decapitating sweeping blades for trying to knock off a jewelry store, so these sorts of traps that threaten death and injury seem to be limited to war zones.
According to the random dungeon placement algorithm in BX/BECMI D&D, one in six rooms not containing a planned encounter should be a trap. That's a lot of traps. I know, because I used that for my megadungeon.
I also have been using it for hexes in my West Marches game. But in a wilderness, a trap doesn't often make sense. Sure, there are a few locations that are basically a big trap. But for the most part, I interpret "trap" as a hazard. So pools of parasite infected water, lava flows, quicksand, rock fall hazards, and the like.
I think a lot of dungeons should be designed this way, too. We don't need to be limited in our imagination to pit traps and darts and the like (although that's fine, especially since these sorts of traps are pulpy fun). But "trap" can also mean just a hazard. The natural disaster that ruined the ancient city caused the walls, roof, or ceiling to be weak in this area, and may collapse. Crystals in the cave wall may reflect your lantern light back in your eyes and blind you. A room's acoustics may be such that monsters in another area will hear you and prepare an ambush.
Thinking outside the box, even a set of natural caves can easily have "traps" and yes, I'd allow a Thief or Dwarf to use their detect/disarm abilities to bypass the hazards, if they roll well.