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.
What privacy threat? How is your privacy suddenly exposed by your like or dislike on the post as opposed to this comment?
Essentially you’re giving away a lot more info about yourself than you might realise. If someone who takes an unfriendly interest in you wants to, they can probably find out a lot more info about your habits, likes, dislikes, interests, political views, waking hours, etc than just what you’ve publicly commented!