I think professional trolls, bad faith argument, toxic influencers, lynch mobs, rage bait, and all the other moving parts that make up the Internet’s profoundly toxic political and social activism sphere also did their part. That stuff really exploded in the mid 20-teens.

Of course you could consider some of that a special case of content mills and spam. It certainly can’t be separated from the ad based business model and the attention maximizing algorithms that drive it, since most of that stuff rides on the fact that being crazy or toxic maximizes engagement.