CoP wasn't changed to be more like Disneyland's since Disneyland's doesn't even exist anymore, it's in Florida. It was changed, I believe to make CoP more like the original from the Worlds Fair in 1964. I think they planned, even then, that it was going to ultimately end up being a historical attraction as opposed to a current one.
There was only on CoP attraction ever built, but it was moved 3 times, and each time the show was altered slightly. It started at the 64-65 World's Fair, then it was moved to Disneyland, and then it was finally moved again to Disney World. All 3 versions of the attraction had the 4 main show scenes, the "1900's", "1920's", "1940's" and originally "1960's" and "Great Big Beautiful Tomorrow" played at both The World's Fair and Disneyland, but in both those locations also had a 5th "finale" scene, that you reached by going up a speed ramp to the second floor of the building
What you saw in the final room at DL was the Progress City Model, which was supposed to become EPCOT, but this was the "Great Big Beautiful Tomorrow" Walt Disney was planning, and part of that model is still seen as part of WDW's People Mover
But the Song "Great Big Beautiful Tomorrow" made sense in at the World's Fair and DL because both those versions of the attraction end with a glimpse at the future, or "tomorrow". When it was moved to Disney World the second floor, 5th finale scene, was eliminated from the attraction. It was shorted to the four main "1900's to 1960's" scenes, with the 4 "seasons" added to each and the new finale scene, the 1960's, got updated to look more like the 1970's which went the ride opened in WDW was "Now", This is also when the new song "Now is the Time" debuted, and they've updated the last scene a few times over the years to keep it looking like "Now"
I know the Sherman Brothers complain about "Now is the Time" and like to the say that it was GE looking for a "commercial jingle", but when the show's ending became a scene of "now" instead of "tomorrow" the new song just made more sense with the new version of the attraction