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.
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.