Parler got shut down because the entire tech industry was in full-scale panic mode at potentially having helped Trump incite a riot to interfere with the US presidential election.
As for Discord, Apple actually has special privileges to ban certain NSFW servers they don't like from being viewed on an iOS device. If they were to act "more" to stop child abuse and extremism, then we'd be talking about how Apple is censoring Discord for Android users.
For good measure let's also point out that an App Store reviewer found CSAM on Tumblr and browbeat the company into banning all nudity and porn.
The only constant of tech company moderation is that it's consistently inconsistent. Strictly speaking, Apple cannot permanently cut off every competing social network, because nobody would buy a phone with no social networking apps on them. But they can whisper in the companies' ears and demand they do a certain thing (e.g. Discord's banned-from-Apple toggle). The really big events (Parler, Tumblr) happen because of breakdown of process, not because Apple only acts when people are looking.
As for Discord, Apple actually has special privileges to ban certain NSFW servers they don't like from being viewed on an iOS device. If they were to act "more" to stop child abuse and extremism, then we'd be talking about how Apple is censoring Discord for Android users.
For good measure let's also point out that an App Store reviewer found CSAM on Tumblr and browbeat the company into banning all nudity and porn.
The only constant of tech company moderation is that it's consistently inconsistent. Strictly speaking, Apple cannot permanently cut off every competing social network, because nobody would buy a phone with no social networking apps on them. But they can whisper in the companies' ears and demand they do a certain thing (e.g. Discord's banned-from-Apple toggle). The really big events (Parler, Tumblr) happen because of breakdown of process, not because Apple only acts when people are looking.