At +3, even in the demon halls, I felt the number of traps was lacking
Just to be clear. It doesn't simply increase the number of traps. It adds a chance that a vanilla dungeon floor instead becoms "a floor filled with traps or chasms." It does absolutely nothing if the floor is already flooded, or covered in grass, or any other floor effect. It's entirely possible—due to RNG—to never have a floor filled with traps even with the trinket. If you encountered a chasm floor, that could have been the trinket doing its thing. It does not simply make traps more common.
I forgot that at +3 it's a 100% chance, so I edited my comment, but that still means it might only give chasms by pure chance. Especially if you're focusing on one region like the demon halls. You could have had a couple other floor effects blocking the trinket from doing anything, and then the remaining floors could have all been chasm floors.