This is only true if advertisers can threaten to shift their ads to someone who does suppress content. A court ruling binding all (or at least all sufficiently

This is only true if advertisers can threaten to shift their ads to someone who does suppress content. A court ruling binding all (or at least all sufficiently large) players in the space acts like a (legal) cartel: Customers (advertisers) don't have a choice, the conditions are the same everywhere.