I am a filmmaker and VFX artist and boy are you wrong.
Doing a 4k scan of a film that only ever was scanned for a DVD release is trivial, provided you still have the masters.
Doing the same thing with a film which was made 1995 as a digital animation is anything but trivial. This is not your "I just have to select a higher resolution and render everything"-thing.
- certain visual results might be bound to software versions that are so old grabbing a copy of them and making them run would be a challenge in itself
- there might be manual processes which need to be redone in order to get the final result — IF they have been documented
- there might be file formats in use which are no longer readable, or might be read differently
Scaning a film and retouching it is trivial, redoing a digital animation that was top notch in 1995 is not.
A good example of this was the recreation of Star Trek: The Next Generation in Blu-Ray resolution. The main scenes were still available on film and could be rescanned. But all the special effects (phaser beams, transporter sparkles, etc) had been rendered using late 80's technology. And had to be recreated from scratch.
Some of the model shots also had to be entirely redone via 3D effects, such as the Crystalline Entity in S05E04. Paramount spent millions on this project, which were never recouped as the discs were released just as streaming took off.
Re-rendering source material for a different resolution is trivial.