Something called a fresh start with people not constantly keeping behind their favorited weapons. Bungie wants people to branch out and try new things, and with HoW they saw that didn't happen because everyone was too busy comparing the new weapons to the old, so much so that the strengths of the new weapons weren't given the proper use. Plus it made gameplay bland, joining either strikes or crucible everyone constantly used the same thing. It's nice to have diversity every once in a while.