Imagination, I heartily agree.
1) I think you confuse maintenance and updates. EPCOT would need both. Pirates needs expensive maintenance to keep it mostly the same. Now imagine not only needing to keep it going, but now make it cowboys instead.
2) EPCOT relied on slow-moving diorama attractions. What about that is easy to update when found stale? I don't know if the argument of the timelessness of coasters in the dark is the best here.
3) Yes, the attractions only dabbled in futuristic subjects, but what of the park/land itself? Spaceship Earth and Space Mountain seem eternal, but the rest is just bland beyond what paint can really fix. As for wish fulfillment, Mission Space does it for me- I went up in a rocket instead of just watching a clip of one (see SE, UoE, H.) Who doesn't want to explore the Galaxy with the Guardians? See how far we'll go with Moana? Learn about the Seas with Mr. Ray? Tour Scandanavia with Anna and Elsa? (I do find the execution somewhat less than fulfilling, but the concept isn't as flawed as some make it out to be.)
I'm not at all confusing maintenance and updates. In the last decade alone every Disney park has recieved significant, expensive updates. That is on top of the regular maintenance, which is more or less regular depending on which park you're visiting.
I never said "slow-moving diorama attractions" were easy to update - but keep in mind that in the last 30 years Disney has spent real cash on upgrading and updating even the MOST perennially popular attractions around the world, often more than once - Every Pirates, every Mansion, Spaceship Earth, many Fantasyland Dark Rides, several Tower of Terrors, not to mention entire lands that have been replaced . . . it's part of the life-cycle of a theme park. The need for that wasn't unique to EPCOT.
The myth that guests didn't like the Future World Dark Rides because "the future caught up with them" is just that - recall that most of those attractions spent 80% of their scenes showcasing the history of their subject, anyway. They only got to the Future parts at the end. Their "failure" is much more myth than it was reality. People cite short lines as an indicator of their unpopularity, but these attractions were designed as people-eaters, and eat people they did. EPCOT actually peaked in terms of popularity AND profitability in the early 90's.
Unfortunately, 90's Disney management wanted to get out of the large, expensive, Audio Animatronics extravaganza game in favor of Thrill Rides that were cheaper to maintain. It wasn't because guests were demanding Horizons be razed for a Simulator. It was because Disney knew the simulator would be cheaper in the long run and hoped guests would go for it. The Future World Dark Rides left us because of financial greed. So they mowed down most of them and set up less dramatic replacements, and look - the park has bottomed out in terms of popularity and profitability, only being propped up with foodie festivals and needing a hugely expensive near-top-down relaunch. The bait and switch didn't work.
Now Spaceship Earth continues to get an update every 10-15 years that lightly refreshes the ascent and makes bigger changes to the descent, and no one bats an eye because that's just something that's done to keep most long-running attractions feeling fresh. I'm not saying that all of the OG Future World attractions should still be with us in 2021, but many of them could have easily connected with an audience without being taken down to the studs. But, as with The Great Movie Ride, it seemed cheaper to start from scratch, so they never tried. And now they're paying for it anyway.