Some pains may be readily removable, some may not. Sometimes the distress caused by pain (or by focussing on the pain) can be relieved (or at least attenuated) by engaging in pleasurable activity (e.g. Epicurus on his deathbed).
Sort of similar to pleasures in that respect. There's always a context that is going to have great influence on when and how you address relieving a pan, just like how you address pursuing a pleasure..
To me that's another reason why "Maximize Net Pleasure" works as a statement of the target while "Minimize Total Pain" does not. The focus by which you triangulate to reach the goal is the "net" -- not prioritizing removal of all pain as the prime directive.