The problem is that those communities chose to use Slack. And now they're locked in to a proprietary protocol controlled by a single company with perverse incentives for censorship.

In prior years those communities would've chosen IRC. But nowdays everything has to be pretty hand hold your hand for you (ie, host your images, assume you know nothing of how to participate on the 'net by yourself).

It is a zero-sum game. And Slack has done the embrace, they done the extend, and they've started the extinguish (by cutting off IRC bridges).