Is there any reason why things gravitate towards being web-centric, especially Google-centric?
Seeing that Google's browser policies triggered the LE change and the fact that most CAs are really just focusing on what websites need rather than non-web services isn't helpful considering that browsers now are terribly inefficient (I mean come on, 1GB of RAM for 3 tabs of Firefox whilst still buffering?!) yet XMPP is significantly more lightweight and yet more featureful compared to say Discord.
Google dominate the space because they have an active, robust trust-store program that they manage well. Apple the same. Mozilla and Microsoft too (though to a lesser extent).
If any ecosystem - such as XMPP - wishes to, they could start their own root-program, but many simply copy what Chrome or Mozilla do and then are surprised when things change.