Because Explosive Conflict is, relative to the other Storymode Operations, insanely difficult and intentionally so. I'd actually say it is harder than Nightmare KP/EV. It really is something that Pugging is a recipe for disaster with. If you have 4 people in a guild and you get 4 randoms from the fleet to finish the group and everyone has voice then it is doable but a pure LFG group? No. No chance.
As for doing HM EV/KP in Battlemaster - it's perfectly fine and doable. Yes, Columi gear has a slight edge but it isn't significant enough to prevent you clearing the content and we've run groups with 3 in BM (or worse) with no difficulties. As most PVPers will have at least a couple of bits of War Hero alongside their Battlemaster those pieces balance out the difference (especially if augmented.) PVP gear is perfectly fine for HM EV/KP as long as you know how to play the class and not to stand in stupid things.
I know that it's harder, that's why I suggested to put in an easier version of it.