Imagine if those items were obtainable via secret achievements and missions in the game. Say if you get the Sweeper Bot emote for clearing all of the story/adventure icons off your map. Or you get an emblem, ship, shader for completing a raid on prestige with not a single player dying, how meaningful would those items be now? Players want something to remember thier achievements to either show it off to randoms or their friends. I remember in Destiny 1, the aww I felt when do seen someone with a flawless ornament. That was something that could only be obtained be completing one of Destiny's most difficult challenge, and those ornaments showed that off. If you seen someone with a full set of Trials- ornaments, you knew they meant business. These also could lead to loads of more gameplay opportunities to get yourself engaged in. The Sweeper Bot example may inspire someone who is not interested in the more, to go through all the story missions and adventures because they want that emote. They might even enjoy themselves. The prestige raid example would add tons to do in game. You may really want tat ship, shader, emote, etc. and so you try the challenge with your friends, only to fail because you're not powerful enough. That would promote going through the other  activities to become more powerful and then try again. Eververse takes all of this potential away and it is severely limiting and hurting was D2 is capable of.