Mostly because Snowden and his image and how it was done make the whole thing much more believable and has more impact in US and Europe then random anon disclosures.

Who knows what his motivations are, they very well maybe noble. Enemy of my enemy is my friend kinda thing.. and when you face US gov power you need powerful friends. He saw what happened to other whistleblowers.

In the end whatever the story is I think he did a great thing for the republic in the long term.