Even simpler than that, "As a YouTube creator, you should remain responsible both on and off the platform. If we see that a creator's on- and/or off-platform behavior harms our users, community, employees or ecosystem, we may take action to protect the community."I would imagine lots of advertisers with large budgets have told YouTube that they don't want their ads to appear in/alongside Brand's content, and that list will only get longer each day.
From their perspective, I guess it's simpler to just stop all ads for now.
I have similar issues, on a far smaller scale, on a near-daily basis with NSC and ads.
That's from YouTube's terms of use. They're a private company, and whether Brand and his followers like it or not, they are simply enforcing the rules he signed up to.
YouTube demonetize videos regularly if they pose any threat to advertiser relationships as well. This can be for copyright infringement, to something as simple as swearing. Basically, they've always been protective of their brand, they enforce it all the time, and I'm sure that whilst many think this is a targeted, almost political act, the reality is it is nothing like that and consistent across the platform.