That's because On The Trail lasts so long that it's not actually valuable [in-run] for most of the duration players have it. Other than L12 Battlefield, how many other zones do you spend > 40 adv in?
(how many other zones do you spend > 20 adv in, anyways? airship, desert, and... uh... maybe a zone for powerleveling?)
Relevant: r19909 adds a nopvp attribute to a few effects known to have this property. In line with some of the other session log prints that have been included with these changes, in the future we could add a warning when we see a nopvp effect decrement after PVP, or indeed an event not yet marked as such not decrement.