They are released very quickly if they fit the desired political narrative, just look at the buffalo shooter and how quickly every major news article dove into his manifesto as soon as they got their hands on it. If and when it can be used to promote a specific view it is released, if it doesn’t promote the correct view it sits for a while until they can figure out how to spin it or the hype dies down and if it hurts the desired view it is blocked like this one.
I would also suggest that you never speak or write any of these assholes’ real names. The notoriety is what they seek and every time a stranger mentions them by name they get their wish.
The media are absolutely working together to push specific political viewpoints. This specific manifesto being blocked fits perfectly with the openly stated political goals of the majority of media in the US.