That's because all they care about is use. If you don't choose to rotate on your own, they will force you to do it. Look at pulse rifles up to the latest nerf. They had a huge buff a few months ago - and it was totally unnecessary. Red Death and several legendary PR's were doing just fine. They were buffed to push people into them and away from HC's, which had worn out their welcome. Bungie does it over and over - they rotate the meta intentionally. Heck, remember them posting IB usage stats for AR's - after they had placed AR bounties in IB? Kind of stacked the cards on that one, right? This is no accident. It's planned.