Because at end game or any of the harder content, the last place you want to be is up close to most enemies. Fusion Rifles offer a great damage alternative that can be used from a pretty good range away. That's not going to change even with the range nerf. Snipers overall out perform both weapons and allow you to take down enemies quick and efficiently from distance. Personally I don't think the 2X damage thing is going to help. If you are playing anything at level 30, or the nightfall, or any of the harder content, Knights, Captains, Stealth Vandals, etc. are still going to be able to kill you in like 1-2 hits up close regardless of how much damage your shotgun does. Hell, Psion's can one hit you at level 26-28 with their melee attack, and then when you add in all the burns and modifiers in most of the harder stuff, it just doesn't make any sense to use a weapon that puts you in such risky territory on the battle field.