When "Who Does What?" Becomes "Who Cares?"
The activities that fall in-between work units can be vital ones and the fact that they are unaddressed can add to their importance. If the various parties knew of the neglect the situation might be improved and yet often the ignorance is calculated.
Each side suspects that the other is not handling the matter but chooses to sit on that suspicion, possibly out of laziness or the desire to avoid a confrontation. I've seen departments that kept such suspicions for years even though a resolution of the question would have improved matters for all concerned. The ability to blame was more important than proper performance of the mission. Both sides were contending for the award of "Who cares least?"