Because none of those things have the force of law backing them.
Academic censorship? Start your own journal and publish there. Religious censorship? Start your own church and gather your followers. Forum censored you? Start your own website where they have zero say about anything and write about whatever you want.
Government censorship? You are screwed, and you go straight to jail if you try to break free and start your own.
Because not everyone who can write an academic article also has the ability to establish and run an entire publishing business.
Just because they technically could doesn't mean they realistically can.
Academic censorship? Start your own journal and publish there. Religious censorship? Start your own church and gather your followers. Forum censored you? Start your own website where they have zero say about anything and write about whatever you want.
Government censorship? You are screwed, and you go straight to jail if you try to break free and start your own.