If your channel covers certain taboo topics it can be "demonetized" which means no revenue from Google. Those channels often have other sponsors.
That almost never happens. Rather, individual videos are demonetized- or deemed unsuitable for all advertisers. In fairness, that can easily happen to an overwhelming majority of a channel’s videos, but it is important, IMO, to speak accurately about what is going on.
Source: I have been a full-time YouTuber for the last seven years. I publish content that often toes the line between suitable for advertisers and not.)