Water sprinklers to fight fire above false ceiling "pockets "

Good Morning all
In NFPA 13 it is stated that if distance between slab bottom and false ceiling is 900 mm or higher additional sprinklers will be installed to protect this "pocket " above false ceiling .
The conditions under which those sprinklers should be installed are not clear , i.e. when it is must and when it is optional .
If we have no thing other than steel pipes and fireproof materials , why should we spend this extra money .


(1) The total volume of the unprotected ceiling pocket does
not exceed 1000 ft3 (28.3 m3).
(2) The depth of the unprotected ceiling pocket does not
exceed 36 in. (914 mm).
(3) The entire floor under the unprotected ceiling pocket is
protected by sprinklers at the lower ceiling elevation.
(4)*The total size of all unprotected ceiling pockets in the
same compartment within 10 ft (3 m) of each other does
not exceed 1000 ft3 (28.3 m3).
(5) The unprotected ceiling pocket has noncombustible or
limited-combustible finishes.
(6) Quick-response sprinklers are utilized throughout the
compartment.
8.6.7.3 Sprinklers shall not be required in skylights and similar
pockets in accordance with 8.5.7.