OOTS #1220 - The Discussion Thread

[Wannes]

I concur. Also, I doubt that the tribe of Bigbears who have been attacking this Dungeon for years, if not decades, or even generations never noticed this trap especially if it flashes light like that at the people who aren't the ones who set it off.

Or the ones that did noticed it and disarmed it completely (and not temporarily as Haley did) didn't see any effect at all from the disarming. Maybe only the temporary disable has an effect, as a sort of "trap-within-a trap".
So they thought "meh, we can just ignore it if it makes no difference", didn't think about temporarily disabling it and thus don't see any use in mentioning it any further.