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 has simply has no chance of gaining widespread adoption in such a competitive landscape. This is why it is very difficult to justify pouring any significant resources into building a decentralized chat app, because too few people will ever end up using it to justify the investment.
For what it's worth, I am the author of a decentralized messaging app myself [1], and have spent a lot of time thinking about stuff like this, and eventually reached this unfortunate conclusion and decided to leave the project at the prototype stage.
For what it's worth, I am the author of a decentralized messaging app myself [1], and have spent a lot of time thinking about stuff like this, and eventually reached this unfortunate conclusion and decided to leave the project at the prototype stage.
[1] http://toc.im/