What are you talking about? Eureka is more future-proofed than Bozja. The only thing you need a group for is BA, and it's not super hard to find them - 4 YEARS later. The entire rest of Eureka can be done solo if you want to, especially with the +300% Echo buff. And you don't need BA for the Relic/Armor. The "super-final" stage that requires BA doesn't change the appearance and the only thing it does is add Eureka-specific stats, something meaningless to you if you don't like and want to continue engaging with Eureka.
Bozja is far worse in terms of futureproofing since it has both CLL and BA and Dal as bottlenecks, and they're further bottlenecks to the Relics as well, since the only alternative to get the parts for those steps are PotD and HoH with low drop rates, which are hard to solo as well (it's the higher floors that have decent drop rates for them, and you can't random que for those).
Except it isn't.
Whenever I hop into Eureka, I see people in it. Same with Bozja. If you play on peak times, you will often see >40 and sometimes >100 people in those zones. While it does happen that there are times it is less, in the case of Eureka, we're talking 4 year old content (Hydatos) or even older than that (Anemos) still being pretty well used.
How many people did you see running Eden 3 normal last week?
Content, in general, decays over time. But Eureka in particular has had incredible longevity due to the dedicated community and unique nature of it. Bozja was less popular, but is still pretty well played. Compare that to raids released during that time and you'll see that your argument would more support removing/stopping adding raid content than it does not having Exploration content.
.
Not all content is for everyone, that's true. But that's WHY you have different kinds of content - for the people that enjoy it.
I've never done an Ultimate, yet they spend massive Dev resources on those every expansion.
I don't have a Static, so I don't do Savages. I've done 3 at level and maybe 9-10 total clears across those three fights.
Does this mean they should stop adding Ultimates and Savages?
No, of course not - because some people like that content, even if people drop it like a rock as soon as the next major patch comes out. Compared to that, Eureka/Bozja are FAR better content with FAR more longevity.
Also: In case you were unaware (somehow?), Eureka has the Echo.
Did you really not know this? Go zone into Eureka right now. Mouse over your buffs. See that Echo there? It has the very thing you say it doesn't have.
.
So yes, we DO need another exploration zone set.