Because they straight up stopped spending money on the attractions to make them relevant. There should be a set timetable for updates and refurbs but everything got stale instead.
And that's very far from being a "only here" situation. Take a look on Disney's social media anytime something imagination comes up. 90% of the posts are either "bring back the original" or "bring back Dreamfinder" or even people sharing pictures of the D+F meet and greet. Nearly everyone in my age group remembers the original because it was vastly superior to what we have today. The literal only redeeming features is the fact Figment is still there and "One Little Spark" lives on. Do I want the original back? I guess. Would I rather have something brand new but in the spirit of what made the original Imagination so great
and D+F? Yes.
Riding the original and coming back to the 2nd version was pure shock. Little me easily remembers the cast working the attraction looking depressed and my parents with their mouths wide open when the lights came on and it said "get off". The lack of a catchy song, random crap set pieces, and the purely unnecessary explosion "jump scare" at the end. It was as low effort as Cedar Point was at taking care of Disaster Transport's theming. Came back 2 years later and my reaction was "still pure
but not as bad as the 2nd version". The ride barely encourages imagination and they shove it in your face the entire time. I'd call that a failure for a ride based around imagination.