I believe Disney and other big studios stopped their 2D animation in the 2000s due to all the competition from animated TV shows and popular anime shows that were being distributed during this decade. It was a good decision from the perspective of executives and shareholders of these studios, they would be able to focus their resources on other projects that would bring in more profits. But bad for the employees that would have inevitably been laid off. Adult themed animations like The Simpsons (1989) and Rick and Morty (2013) are still very popular today. The next generation of shonen anime like Demon Slayer: Kimetsu no Yaiba (2019) and Jujitsu Kaisen (2020) are proving that they can create great anime movies.