Yesterday it was because he stepped down as director and writer of the Batman film so that we he can focus on the acting, which must mean he wants out of the franchise because it's a "mess".
Today it's the studio is planning to can him because he's too old, and also because his brother jokingly said he's leaving.
Tomorrow it'll be an anonymous source of a friend of a friend who used to know the person who watched Jennifer Lopez's dog on occasion, recalled that the dog sitter once told them that Lopez told the dog sitter that Ben once told her during dinner that Batman is his least favorite superhero while they were dating 15 years ago. Now if that's not evidence that he's leaving the DCEU as Batman, I don't know what is.
Like you said, if they want to try and subvert the DCEU, they should find a new angle instead of continuing to chase this Affleck-is-leaving fairytale. However, I mean you can only cry wolf so many times and so frequently, before people eventually start to say bull*****, whether that comes in the form of finding new angles constantly, or constantly coming up with new reasons within the same angle.