Indeed traps do technically have a rating which determines what depths they might appear at, but traps are non-part items and the info window doesn't show ratings for any of those because most don't have ratings at all. This would require adding a separate classification for traps and further complicating the part comparison architecture, which I don't really want to do since it's not incredibly helpful, since you can't use trap ratings like you can ratings for attachable parts.
You can get trap ratings by exporting gallery data, which sometimes includes extra values that the in-game window doesn't have.
