Thank you for bringing this to our attention, Explorer. Such anti-Kind "purges" on YouTube -- and just about every other social media forum you can name -- have been common at periodic intervals. What is responsible? I suspect the same thing that has usually been responsible: the incessant use of the flag buttons by censorious members of what has been called the "pedo police." Any time pro-MAP voices start becoming prominent on any given online forum -- be it Blogger, Reddit, Twitter, YouTube, etc. -- the legion of antis who are always reliably present take steps to flag every single one of them.
As we all know, the administrations of these forums rarely actually conduct a thorough investigation of complaints made by viewers. They instead tend to simply default to favoring the complaints of the complainers, sometimes in almost knee-jerk fashion. They will tell the owners of these blogs and channels that their material "violates the user terms of service," which is easy enough to do, since these terms always include the stipulation that material deemed "inappropriate" or "against community standards" will be removed. What does "inappropriate" and "against community standards" mean? That is very simple, too: both mean pretty much any message, topic, or viewpoint that offends enough readers/viewers and the administration themselves, as well as potentially turning off the many corporate sponsors these fora are increasingly coming to rely on for monetizing their platform. These are deliberately nebulous terms that loosely translate as, "offend us enough, get hit with enough 'flags' to indicate a sufficient number of viewers are not willing to tolerate your views, and threaten to drive enough of our high-paying sponsors away... and you're outta here."
This is nothing new, and eventually these voices will regroup and find their way back, as voices of reason and defiance have thankfully been a persistent lot (social progress of every sort would never have been possible if we weren't). But it will be a while before these waves of censorship are halted altogether, because we all know that censorship is the most potent tool society has in keeping unpopular views from being heard and considered enough to possibly become popular.
There is also no doubt that the recent growing spate of non-Kind voices standing up in open public defense of MAPs is signalling a significant turning point in the debate that is panicking many antis and beneficiaries of the present status quo, thus invariably mobilizing them towards yet another one of those periodic information purges. The alternative to the censorious purges is to challenge these voices fair and square on the public platforms, and when attempting to shout these voices down with a combination of emotionally-charged insults and threats doesn't work, then it's time to resort to dirty pool tactics like cutting off our access to the public eyes and ears. And since they have the advantage of controlling every aspect of the media, why should they engage us fairly if doing so is not shutting us down?
In other words, it's just business as usual at YouTube, Twitter, etc.