[bsder]

> But I do think Mastodon and Matrix / Element all have a marketing problem. It's seems to be "here's a clone of a service you use but you own your content".

Well, Slack and Discord have the ability to throw around money to solve that problem. Open source projects mostly don't.

So, open source projects have to hit some nerve and then slowly grow into useful and then a dominant project. See: the trajectory of Blender.