Its actually not quiet that simple. Yes mining and similar things are contributing to it, but the major issue is actually related to diplomacy and corporations and alliances.
If players are using the lp system for isk optimization the system should have lp gutted, and then the credit values buffed. when we (developers) create systems like this is to help enrich the reward system make things less “stale”, however optimization of isk out of this does just that, makes it stale. LP system should probably randomly assign a reward on completion sort of like obtaining an item after beating a quest and set up the levels to assign specific drops (like l5s giving RNI or VNI) (chance based) or maybe a choice between two or three things? something that needs to be talked about.
This will allow players to earn isk like they should for missions and doing missions is about isk but one of the fun things that comes from it is the rando rewards. much like mining provides social interaction as one of its “by products”.