I don't understand the appeal of these things. For games that are not skill and/or reflexion oriented like Diablo once you've finished the campaign you have exp

I don't understand the appeal of these things. For games that are not skill and/or reflexion oriented like Diablo once you've finished the campaign you have experienced what the game had to offer, a good hero journey. Replaying for other classes, missed side quests or simple monster bashing can be fun too. But what you describe seems not to be the satisfaction of discovering, only on collecting and checking boxes for the sake of it. This is akin to trying every parameter on a slot machine and trying to get every combination. That's very close to gambling addiction or OCD for me.