I don't agree with your basic assumption - google doesn't get money from publishers, but from advertisers. If they ban one publisher, the ad may get clicked

I don't agree with your basic assumption - google doesn't get money from publishers, but from advertisers. If they ban one publisher, the ad may get clicked somewhere else. Let's call this metric 'ad fill factor' - how many different ads does google have for this content and traffic? When some niche is getting near the point when there's no enough ads for its traffic the marginal value of website becomes exactly zero. At this point, banning accounts and taking their earnings makes financial sense.