Why don’t people just…?

This is only looking at another siloed alternatives, while ignoring federated protocols such as XMPP or Matrix. The problem can't be solved if an infra has to be the single point of failure:

1. It grows too large then it will get corrupted, e.g. Twitter/Reddit/Discord turning for surveillance capitalism and GitHub going for license laundering. 2. If it doesn't have many users it's likely to be discontinued.

On Matrix for instance, the room is replicated on all members' homeserver, and any admin can create a room alias (e.g. @foo:example.com creates #project:example.com, @bar:example.net creates #project:example.net). Like with emails, conversations can still go on even if some members' server goes down (and unlike mailing lists which are host on a single endpoint, there are multiple aliases).