@wjmaggos facts. This is especially apparent because they aren't really doing anything to endorse turning Fediverse sharing on.
Their employees discuss it sometimes and there's a button that works, but they do go through great lengths to seemingly convince you that doing it isn't a *good* thing.
They're just doing it because it'll give them an edge in case it takes off like e-mail. If it does, they might promote it and discuss it more positively. However, until that happens, they probably won't. Adam Mosseri already confirmed that they don't ever plan to remove the "opt-in" part, which basically kills the idea of open communication.