The details as to why and how are explained in the second half of this article (unfortunately in German): http://m.faz.net/aktuell/feuilleton/medien/edward-snowden-un...
In short it is a copyright fck-up on behalf of the German TV channel that made a mistake when transferring the copyright from its subsidiary to itself. The international distribution right is now stuck somewhere in Nirvana in between the companies, which is why they aren't able to give/sell the video to other international TV stations like CNN, for them to show it.
At least this is my legal understanding of the situation. You can use a proxy like zenmate and see the video here: http://m.ardmediathek.de/Edward-Snowden-interview-in-english...