I was born too late to witness popularity of XMPP as a decentralized instant messaging protocol. When I started to be a "conscious" user of the Internet, such services already became centralized, so I don't really remember those times. As I follow the development of projects like Matrix, I wonder what has made SMTP such a stable protocol that has stood the test of time and what is the real reason we don't use XMPP (I mean, we do using Whatsapp, but as a part of closed ecosystem).
Is it only that XMPP was overcomplicated and if managed better it would survive? Or is it something else?
The environment outside of major providers was (it definitely is) kind of janky. If you can set up a server application it's not hard but it's not exactly easy to get started, or get people on it without handholding (from my own experience).