I think you might be having difficulty grasping the idea that people have marketing budgets and if say the ceo of a company you advertise on very publicly endorses hate speech it does create a brand management problem.
You want your products to not be associated with things like, say, racism, which are kind of “yucky” to a lot of people.
As a result you might refocus spending. If a bunch of people do this at once this doesn’t mean there’s collusion. For example, during a thunderstorm you might see less people outside. This isn’t because they all colluding - people don’t like being struck by lightning. Similarly, companies don’t want their brands to be “yucky” to the average consumer and often its just a matter of moving the ad spending to another platform without the baggage.
You could ONLY limit this effect by banning advertising entirely.