It just doesn't have much weight when the overwhelming bulk of their revenue comes from subscription services. It's cool that they're experimenting with this, I guess, but it doesn't exactly instill faith that the pricing model is sustainable. It's like how Google can afford to offer a bunch of free services because of the bazillions of ad dollars subsidizing everything.
Does anybody use it? There was a lot of hype on Twitter when it first came out and I haven't heard a single thing since then. Who wants to install that on a VPS and be responsible when it goes down when they could just use a Discord server or Slack?
This definitely depends on the use-case. But not having to rely on a foreign service and owning your data is huge for many people.
Additionally slack is super expensive for a paid tenant that does not delete your chat history. And some day in the future Discord will surely enshittify their free options too.