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.
if theres a way to link your username to an email address, Meta could, for example, create an instance and scrape all that info and attach to your shadow profile, and depending what kind of things you upvote, they could infer your political opinions, sexual preference, location, hobbies, etc.
This circles back to if you are that concerned about privacy
Its seeming like a lot of people want privacy but aren’t willing to take even basic steps to protect their own privacy, instead wanting someone else to do it for them.