I'll try to give the simplest possible explanation that tries to be value-neutral and avoids getting bogged down in an ethics debate: copyright. Movies are intellectual property; political information is generally not.
More worryingly, how hard is it to create fake data? People are leery of accusations by prosecutors, far less so of "data". Video and audio evidence can even be faked now.
For instance, a bunch of your emails get dumped (all of which are indeed your real e-mails). But then there's one (fake) message to a random email address nobody knows the identity of, "Yes, I'd like to buy 100 kilos of coke and I need help laundering the money after I sell it." Who is the burden of proof on? You to prove that you didn't write it? Or them to prove that you did?