Having a fast way of getting announcements to people is important. Everyone from the WHO to official government announcements to musicians with a new album to activists announce(d) things on Twitter. For that purpose the first and foremost thing is maximizing the reach of the announcement.

Now there are a myriad of better platforms for this (irc or a mastodon instance owned by the org) but quite frankly they will never have the same populations as bluesky or Twitter (in the short term) because they are a as you put it a "good" social media that isn't just about infinite growth.

Be glad that the billionaire actively and openly trying to censor the world is losing out to the billionaore that will leave it alone and sell out again in decade or two. And on the side mastodon picks up the more traditional social media role among those in the know and maybe one day sustainable growth will make it the biggest fish and can take over from the replacement for the replacement of bluesky as the primary announcements channel.