It's not bannable because it's more of a glitch and unbalance than an exploit. It'd be like making the original Vex usage (the one where it still fires crazy fast, but it's a 3 body shot kill) a bannable offense. Lag switching and manipulating the network for nefarious means? Bannable. Making use of an internal bug/glitch that Bungie goofed on? Not bannable, but poor sportsmanship, and one that I don't do.