Earlier quoted context omitted.
As much as I agree with your overall sentiment, the sad truth is that centralized architectures enable many of the UX affordances that users take for granted today in a modern chat app, many of which are much more difficult, sometimes simply impossible, to implement in a decentralized architecture (think features like automatic contact discovery, offline messaging, etc). Without some of these affordances, a chat app…
What kind of things are impossible?
Toc's original goal was to be a decentralized messaging app that makes no compromises in terms of UX compared to a centralized messaging app. Toc managed to tackle decentralized cross platform sync, but to this day I still have no idea how to approach automatic contact discovery and robust offline messaging.