Hideaki Anno, creator of the Evangelion made a post about Gainaxand the reasons why he left his former studio.
Annoco-founded Gainax with colleagues in 1984, and during its most prosperous period, the studio produced memorable animations such as Gurren Lagann. Since 2006, the director has worked at a new studio called Khara, and has acquired some intellectual properties that belonged to Gainax after a financial dispute involving unpaid royalties and a loan taken out to try to keep Gainax in operation. Neon Genesis Evangelion is among them.
Because of this, Anno said he was extremely disappointed by the way the arrest of Tomohiro Maki, the current president of Gainax, was reported, linking Maki to him and Evangelion. He emphasized that "there is no one currently involved in the production of Evangelion at Gainax" and that the person arrested was someone who joined Gainax only a few years ago and never had any involvement with the anime. As president of Khara and the original creator of Evangelion, Anno stated that he feels "a responsibility to protect his work and his employees" to ensure that the franchise will no longer be associated with Gainax.
Anno mentions that since the early 1990s there had been plans to produce Evangelion at another company, due to concerns about the workload. At the time, Gainax ended up partnering with Tatsunoko Production to produce the anime.
Tax evasion:
Around 1999, Hideaki Anno discovered that Gainax was evading taxes and even appeared on TV to apologize on behalf of the studio. He noticed discrepancies in employee salaries and claims he gave the company chances to resolve the issue, but felt they didn't listen. Therefore, he decided it would make more sense to produce the Evangelion films at another studio, believing it would benefit the industry.
However, since he couldn't find another studio he trusted enough, Anno formed Khara to control production costs and provide adequate salaries.
Finally, Studio Khara will release Evangelion: 3.0+1.0 in Japan on June 27, 2020.
Source: Diamond Online