Chris Orr puts his finger on the studio's secret to success: "constant revision and incremental perfectionism":
It's a luxury unique to animation, though one of which few animators take comparable advantage. Live-action filmmakers are essentially slaves to a shooting schedule. They go in with a script, storyboards, etc., and come out, several weeks or a few months later, with the footage they will assemble into a motion picture. Once the sets are broken down and the cast-members scatter to their subsequent projects, that's pretty much that, barring a relatively rare, extremely costly re-shoot. Any subsequent "eurekas!" on the part of the filmmakers are likely to be unrealized.
(Video hat tip: TDW)