>GFI outlets don’t trip based on moisture, they trip on a difference in the current between the line and neutral.

Get enough moisture between hot/line and ground, and you'll have that difference in current that'll trip the GFCI. That principle may also save someone's life - e.g. wet feet in bathtub, hand on faulty device plugged in that contacts or leaks hot to the person's hand, flows through them, into feet in tub and ground ... again, moisture, current imbalance between line/hot and neutral ... and ... it trips.