There's a bit more nuance to that. Some advertisers can choose to put ads on videos that are labelled undesirable. But because there's less advertiser demand for ads on such videos, they're generally very cheap.
There was a time after I took a media class where I had insomnia and watched a lot of late night TV. I knew about targeted advertising, and the kinds of ads on late night TV at the time… oh boy. The lowest quality camerawork, dialog, and product. For a while I felt insulted, that they thought I was the target audience for this schlock. Then I realized that no, this is just the cheapest ad slots of the day, and so they are running bottom of the barrel ads during this time.
So I guess we can expect to see wannabe-Billy Mays ads on demonetized shows.
