It's progression think about life, nothing lives forever, everything goes away eventually. It's refreshing to have to use different weapons, it's a new experience. And with any game that has levels and classes, when an expansion comes out the previous weapons are replaced with stronger ones. That's how it is, I'm sure it also has to do with gjallarhorn being just about everyones goto weapon for like bosses and solar burn things, it has also prevented a lot of people from raids and PoE for not having the jellyhorn. It essentially divided a community into "people that have gjallarhorn" and "people that don't have gjallarhorn". I'm all for a new experience and I'm okay with leaving gjally behind.