I believe there are procedures/checklists for placing aircraft in and out of storage which are different than those used for normal operation, because the conditions are different. It is my understanding that this directive is an additional check that would be performed during the typical storage procedures.
I think the issue here is the lack of flight-hours. These parts were designed and specified for an in-use plane, not one that sits around.
An airplane is an extremely expensive asset and they are typically almost constantly in service. It's very rare for one to be idled for months at a time.
yes - this is related to non-routine maintenance. I assume operation prevents moisture forming that can corrode. Storage for several weeks or months means this is like a more stringent used car "road worthiness" inspection.
Surely there's some sort of chart they've made for all these parts and how fast they're allowed to decay, given some number of flight-hours?