Why the accumulation is invisible until it is not
Dust on an exposed beam six metres up is not visible from the floor and builds over months without anyone registering it. The first symptom is usually indirect: a fine film on stock, a surface that looks dusty again within a day of cleaning, or a visible fall after a windy day when a roller door was open. By then the reservoir is substantial and a routine wipe below does nothing.
That delay is what makes a stated interval necessary. Left to observation, high-level work happens when a client finally notices, which is well past the point where it should have occurred. A recorded interval with a due date means it is scheduled on the basis of how the surfaces behave rather than on when someone happens to look up.
