I don’t think it’s a matter of “the fediverse isn’t built for that kind of privacy”. The fediverse does have privacy post options all built into the platform you’re using. Mastodon allows private posts, only those who follow you. Kbin is a mashup of Reddit style threads and microblog timeline posts.
Kbin was developed to show upvotes and boosts as those are synonymous to other platforms like mastodon as favorites and boosts.
The lemmy platform is more “private” that on lemmy posts you don’t see this as much. With federation and interacting similarly between ecosystems you start seeing the minor differences.
I do think that changes as possible and that is what makes the open source of the platforms we’re using to be important and requires community input for improvements and suggestions as a whole.