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.
The difference is on Reddit/Twitter/FB/etc the only people with that kind of access are employees hired by those platforms. It’s out of your hands, but not public data.
With lemmy, any random person can spin up an instance, federate it, and view that data. It’s openly available to the public, just with a few extra steps.
A lurker on reddit leaves no public info, just a username and an account age while still being able to up/down vote.
That same lurker here would leave a trail of up/down votes that can be viewed by anyone who knows where to look.