No, and they won't. Reasons certainly include monopolization of the information but also protection of the leakers and others. Protecting the sources is one of the key things good journalism has to do.

some digital proof would be more convincing, like "at time X we got archive with merklehash H of all documents (https://opentimestamps.org/), and this information Y is from this source file hash F proved by this tree T".

For proving what? - I haven't seen anybody that their reports are inaccurate. The only possible critisicm might be that they maybe don't tell everything to protect individuals. (Which I don't believe they do) But even there it won't help if they publish everything as we can't have a prove it's everything.