Because it's littered with SUROS Regime's, a few Vex mythoclast, and various other weapons that make the "Iron Banner" not worth it to play if you keep on getting killed every 5 seconds. Not only that but Bungie has done an ABSOLUTELY TERRIBLE job at giving players an incentive to go through the madness that is the "Iron Banner". Its really just a slaughterfest for those who were lucky enough to buy the Regime from Xur or those who have poured in an ungodly amount of hours into the game. At the end of the day, its just a poorly made event with little thought put behind it like the rest of the game.