Which was completely unrelated to the content you actually did for that relic, so irrelevant on that topic. In fact, the Eureka weapons are more related to Eureka lorewise, especially the very final stages, that any previous relic to the content they asked you to do.
The Zodiac and the Anima were separated, the Eureka weapon isn't (In case the name wasn't clear). And, like I said above, there is a lore connection between the two. Also, the Zodiac was the only weapon available in 2.x if you wanted to keep the (almost) max ilvl at each patch without raiding. This was not the case in HW and SB. And, finally, the Anima had a step tied to Diadem and would have probably had others if Diadem didn't fail spectacularly.
People don't go into content just for the content, you have to give them a reward for that. It's the same for everything. Remove gear from Savage, and it will be on life support after the first clears.
Except that, no, not everyone does the relic. Right now, the number of characters having done an Anima is still a very small part of the playerbase, despite being nerfed to death. And I'm pretty sure even the Zodiac is still a rarity, despite it being actually competitive in its own time.
Considering how many people did Eureka despite hating it, just for the relic, it seems priority is a bigger issue for them. Me ? I like the relic, but I only did it because I like Eureka. I would have completely skipped if it was just another tomestone farm ad nauseum like the two previous ones.
In fact, the sentence above is probably the biggest clue on how likely the next relic will be tied to an exploration type content. Because it made people do it, even if they didn't really liked it. So, from a strategic PoV, it was brilliant. The thing, now that exploration content has already been confirmed for 5.x, is to give feedback on how to improve the content.