Two questionable reasons for why videos are blocked in Germany:
- The copyright holder possibly (in contrast to actually) does not allow the content to be online.
- The video contains symbols of unconstitutional organizations.
However, I repeatedly had to circumvent youtube's blocking to watch videos that use original footage from the NS era to illustrate the terrible crimes committed by Nazi Germany. They were blocked due to the ubiquitous swastikas, not due to their message that simply put was: We must never let this happen again.