It's not an easy process to stop maintaining softwares for such large companies.

Flash is still widely used, and so many websites still rely on it that it will take a lot of time to fully abandon it, so Adobe will still have to fix all security issues for years.

Nobody is asking them to build new features, just fix security issues. And Flash is still a supported platform by their designing tools like Animate.

Adobe Animate isn't a new tool, fyi. It used to be called "Adobe Flash Professional". They renamed it in order to distance it from Flash.