> That would seem to imply some overarching legal enforcement regime, rather than law of the jungle.
No, it implies that if you respect the laws of the countries the people you serve reside in, you can choose to follow the law by not serving them, and therefore not having to "do what they say", or serve them, but then by their laws "do what they say".
Regarding effects on Twitter: it costs them money. Their share prices drop and jo-jo a ton when stuff like this gets out. Legally, not much effects twitter, it's not a person after all, and legal departments weasel their way around plenty to make sure a company keeps existing and keeps making money. If it's cheaper to censor some random person on your private platform then compared against shoring up your cyber defences, that's an easy choice for the people in charge with somewhat cartoonish dollar signs in their eyes.
The reality is that nothing is truly isolated from side-effects and circumstances in the world. Even if there are no diplomatic ties, and no physical violence, it's all happening on the same globe with the same internet. So ignoring laws is not always the cheapest way to deal with countries, and not dealing with countries is generally not an option when you're connected online.