A few days ago, all videos on the Blender Foundation YouTube channel were blocked without any explanation.
Eventually, several news sites like Tom's Hardware, Fortune and Daily Dot reported on the issue:
Following that, YouTube replied that this is a technical issue and will be fixed soon.
However, now it turns out that the block appears to be intentional and YouTube demands ads to be enabled on all videos, as reported on the Blender blog.
The Blender Foundation channel isn't the only channel to be affected, another notable example is the MIT OpenCourseWare channel.
Personally, I think this is an extremely worrying development for educational videos on YouTube in general. The two channels decided to not enable monetization, and now YouTube apparently went for some intimidation to bring them in line. I'm glad that Blender decided to publish the sent contract instead of just giving in, hopefully the videos will be able to stay ad-free.