Some players enjoyed getting the new content. Can't blame them for that.
What I wonder is how things look from SE's end. Did participation in relic grinds reduce when they were related to the exploratory zones and that's why they're trying out this method for Endwalker? I know I didn't enjoy Eureka at all so never touched the Stormblood relic. I started on the Shadowbringers relic, decided I didn't like Bozja and left the relic unfinished because I don't enjoy Alliance raids/Deep Dungeon either. If SE had allowed us to keep farming memories in FATEs, dungeons, normal raids, roulettes, etc. I probably would have finished it.
This expansion I get to do my choice of content so I'm back to working on a relic again. If in 6.5, they decide it can only be completed doing a specific type of content and I don't enjoy that content, it will end up another unfinished relic.
I find that a silly analogy.
People have things they like. People have things they don't like. The things they like don't necessarily get stale with time.
Do you not have favorite things from childhood that you still like to do or eat/drink? Aren't there things introduced in recent years that you've tried but decide you don't like? (Or I don't know, you might be young enough that they're all still one and the same.)
Not every player was around when the old content was first released and so haven't done it repeatedly for months on end. It's still interesting to them.
I don't blame people who enjoyed the exploratory zones for being disappointed that there wasn't a new one this expansion. You still have the option of doing other new content added this expansion to get the tomestones for the relic, though. If you don't like any of that, you have the option of doing the content you enjoyed in the past to get them.
Or you could skip doing the relic because it's just another shiny weapon in a long line of shiny weapons that don't mean much of anything by the time you get them completed. Spend your time back in Eureka and Bozja/Zadnor if that was the content that you really loved to show SE that there's still interest in more exploratory zones.