The reason to move on is so we can have more interesting things to play with in the future. The problem with never moving on is it burdens the development team. Their ability to come up with creative challenges and weapons is hindered by the past. That weight would eventually ruin the game. Right now already there is quite a large imbalance between people with certain weapons and those without. Those encounters become trivial for people with those very strong weapons and very hard for people without them. This makes designing encounters pretty difficult. Everything becomes a bullet sponge that instantly kills you. This is due to the outliers. It's not unlike Magic: The Gathering in standard. Over the course of set releases certain cards will be extremely strong. This is fine because in another year or so, they won't be legal. Those format defining cards are removed from the pool so new stuff can be discovered and keep things fresh and creative. The issue is not comparable to an MMORPG. You're right about that. Bungie does not need to follow convention, and they aren't anyway, exotics will still be upgraded. This is non-standard and works alright because of their limited number and often niche application.