Edit: obligatory explanation (thanks mods for squaring me away)...
What you see via the UI isn't "all that exists". Unlike Reddit, where everything is a black box, there are a lot more eyeballs who can see "under the hood". Any instance admin, proper or rogue, gets a ton of information that users won't normally see. The attached example demonstrates that while users will only see upvote/downvote tallies, admins can see who actually performed those actions.
Edit: To clarify, not just YOUR instance admin gets this info. This is ANY instance admin across the Fediverse.
Here's a scenario... Some admins are using data to build correlations between accounts. Linking main account to alternates. So far that I've seen the purpose has been to identify bot activity. A good thing.
The same analysis could also be used to build correlation between a main account that's hard right leaning and an alt-account that may be sympathetic to left-leaning or progressive topics, such as LGBTQ+ rights. Not so much a good thing.
I think it's fair to say that many people will not consider the fact that, literally, anybody in the world can have access to much of this data. It's not limited to your two or three instance administrators.
