One of the ways the community chat services like Slack and Discord are succeeding is by making group control easy. You don’t need to run your own Slack server on actual hardware, you just click a few buttons and have your “server” set up.
There’s a small subset of people for whom “install this software on your server” is a legitimate ask. And there’s a much larger majority who would have no idea what you’re even asking of them. So cloud services have a natural advantage in reaching a broad user base; and combined with the network effect, that advantage becomes overwhelming. Even though I’m in the former group, and could probably run Mattermost on a server reasonably easily, I still use Slack for my day job and Discord for most of my communities. I let Google do email, I let Dropbox sync files, and I still use Facebook and Twitter despite finding them both horrible.
You wrote a post a while ago about how we were signing our lives away to these proprietary walled gardens, and it’s true; but when the alternative is a technical hurdle that excludes most people, the cloud services are going to win. A winning non-proprietary solution needs to also compete in how easy it is to set up and use.
An example that’s quite good at this is Syncthing, which is a tool for live syncing data two or more computers. A bit like Dropbox but without any servers in between. You don’t need to install a Syncthing server, you just install a program and run it – and it somehow manages to get through NAT on either side. It could do with a bit more polish, but it works.