Well, they clearly have a weighted item system. Some exotics are great in very specific situations and terrible in everything else, while others are mildly beneficial in most situations but don't really shine in any particular encounter. Then you have items like gjallerhorn and icebreaker which were just amazing in every situation. Notice how those items arent sold often? They are clearly weighted so that they arent sold often. If gjallerhorn dropped for me, I'd basically stop playing. That's the only carrot I care about right now. Bungie knows that.
It's that can't make too many exotics that are on par with IB jellyhorn because then PvP gets completely out of control. I mean I don't reply care about PvP but there's a lot of unintended consequences when it comes to PvP. It's the same issue with auto rifles. Everything has low impact high RoF because the reverse will always win in PvP (generalized statement, I'm aware).
If it was just PvP you could introduce all kinds of crazy exotics with goofy, op effects on them and it would just make the game more fun. You or those same things in PvP and people get frustrated real quick.
