Maximizing publicity is important, if you actually want to enact positive change as a result of what is being revealed. If everything was released at once there wouldn't be any focused attention and easier for those effected to try and deflect attention.

It's also an interesting way to put all banks on notice for their behaviors, as unless they know more than us they would all consider it's possible that their documents have been leaked.

They've been redacting information in every leak so far.

I'm not sure who could get killed if some bank information is public, but if they have a lot of documents, this could take some time.