It's App Store. It all started with the App Store.

Advertisers are also considerably more picky about the content they're willing to be associated with, and considerably more influential with regard to the content most people see online than they were 20 years ago. Advertiser demands have produced rapid policy changes from the likes of Youtube and Reddit where other forms of pressure have had little effect.

I'd potentially reverse this: 'overt' political censorship didn't start until certain creators started to market their otherwise objectionable content as "political" as a way to bypass existing moderation policies.