You may have noticed that more than a few of the embedded videos on this site aren’t available.
The short version is that YouTube rolled out a new pricing/subscription tier, YouTube Red, and most content producers who monetize their channels need to either switch to the terms under Red, or they need to un-monetize their channels (I think; it may be that they need to let YouTube place ads on their stuff? I see different things.).
The important thing is that a number of idol-related publishers are having their content blocked in the United States right now, and it may be that they never opt to disrupt their revenue flow by changing because, frankly, they’re not making that much money from countries outside of Japan. Which will obviously be a huge loss for us, but life finds a way.