When the disparity in strength is too obvious, it's natural for one party to temporarily avoid crossing swords.
If both sides are evenly matched, rarely do they engage in full-scale war; they often face off for a while, exchange verbal barbs, and eventually disperse on their own.
So...
Unless it's those permanently stationed in the Realm of Death at the rank of school officer, those promoted to school-level ranks tend to actually see a decline in real combat skills.
Their daily focus in cultivation is primarily on the exploration of the 'Dao,' which is essentially 'trudging through the Dao.'
The farther one treads on their own 'Dao,' the stronger the 'Field' they can unleash.
Therefore, the 'Taoist Canon Fragment' naturally becomes its main use as it aids in 'trudging through the Dao.'
Besides this...
The third reason why those at the warrant officer rank rarely use the 'Taoist Canon Fragment' is because it's not of much help in 'Enlightening the Dao.'