These have actual, proven expertise in publishing leaks.
All those new "leak sites" have a trust problem. Although it's likely that most of them have noble intentions, it's equally likely that some of them have been funded by or have been undermined by intelligence services. I wouldn't even trust any open source software that is specifically developed for leaking sensitive information - it's simply too easy to slip an obfuscated security hole in it, and it's not as if the developers could afford regular professional audits.
I suspect some people will downvote me for this, but in highly sensitive matters I'd rather stick to those with a proven track record and evidence of having been persecuted by governments in the past.
To the people who think this is paranoid: It's not. Getting informants or people working on their behalf in crypto projects is the bread & butter of what intelligence agencies do, and it's much easier for them than their usual targets such as foreign military and agencies of state adversaries.