Certain Disney movies only grow in popularity over time simply because they're both good and Disney. The availability of the movie on DVD and streaming services help.
This means, over time, more and more people see the movie than what it's original run would indicate.
And this means more and more people coming to WDW are familiar with the property and are nostalgic for it. This is what happened to Peter Pan and some other one-off non-franchise movies. E.g., Princess and the Frog didn't make a profit in it's theatrical run and, soon after its release, there wasn't much PatF in the parks. But, as time goes on, Tiana has become and more popular. She has her own M&G. PatF is part of the stage show. Tiana appears on HEA. Dr. Facilier is now one of Disney's go-to villains.
UP!'s popularity grows and is a family-friendly IP that sorta fits for DAK. So, WDW is now running with it.