People "don't trust" in the very abstract sense, Mark Zuckerberg. But in a very real sense they don't trust their manager at all, and they know their own manager can see their messages on the "sovereign" messenger. Zuckerberg wants to sell them stuff they don't want on occasion. Their manager ... well they're cheating their manager.
Oh and it doesn't even buy extra security: the platform owners can spy directly through hardware backdoors, they can "update" any app on the phone, and they have the root keys to the secure element, and so it isn't secure to them. And if you look under the covers ... the backend is on AWS? No? Must be on Azure then.
So annoying lots of people, reducing functionality, for no actual security.
Sure sounds like EU governments are behind this ...