It's been argued that FF's are less accepting of the AIT vs. ma and pa kettle, infrequent travelers. I would posit the business traveler/FF is more likely to travel in the evening hours and thus you're seeing a more accurate reflection of the FF's opinion of the use of AIT.

Since the business traveler is also more likely to travel in the early morning hours, I wonder if people on the early morning shift are witnessing the same increase in people opting out as at night?