Let's see, B-pods explode for 2 damage, M-pods for 5, Coolant Pods for 10. Only Coolant Pods deal sufficient damage CASE may be actually relevant commonly... for 45 tons or below as those have internal structure of 11 for side torsos. But such designs most likely don't have tonnage to waste for CASE unless they're going to be utilizing that anyway. And i would question wasting tonnage for one-shot equipment in lighter designs anyway, unless they're specifically meant for tasks where such things are highly relevant. Not to mention a critical roll needing to actually cause a critical hit and it landing on the correct slot if there's padding.
Figure bigger 'Mechs can either tank the hits or their greater durability means much higher likelihood of actually using OS equipment before it getting critted.
If a 'Mech has composite internal structure, CASE (or CASE II) may be more useful if OS equipment is carried but spending weight and slot savings from composite for OS equipment in such case is highly dubious.
(In case someone wonders, rocket launchers and OS or iOS missile launchers do not explode if destroyed unfired.)
Way better solution to mitigate explosiveness of OS equipment is to locate them in legs, if locating them in existing CASE'd location is not an option. Legs are usually well armored, partial cover can protect from crits completely, and without floating criticals there aren't many ways to pierce leg armor in the first place.