There seem to be two responses to this problem: 1) Asserting that YouTube/Facebook/X is not "private" in any meaningful sense: they are acting in the public and affecting the public discourse, so they need to be regulated to prevent them absuing that power. There are sub-discussions about whether that regulation should be a Haugen-style imposition of extra censorship for our own good, or as in this case a need for the regulated effective monopoly to defend why they chose to censor this particular news organisation.

2) Asserting that it is possible to build our own platforms. But then we will see censorship like this at the level of Cloudflare, search indices, financial transaction processors all the way down to ISPs themselves. And that's even ignoring the problem of how to bootstrap (e.g. Parler) into something that enough people know about to make it useful.

I find #2 implausible at this point although I like the DIY ethos of it.

Ignoring the availability of regulation which exists and will be used by someone, is not helping ourselves to a tool that can be effective.

As a direct answer to the question posed by the article: it seems possible that this was a warning action carried out because Novara Media were the sole media organization livestreaming the Assange Belmarsh event.