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.
Source instances can be seized ( https://kolektiva.social/@admin/110637031574056150 ).
UUIDs aren’t “invested” enough. Interacting with a name rather than 08d86062-730b-4081-8c4c-b28bca1713b6 or c4e1261a-087a-448d-bd3f-5c3d8ab28aab is desirable.
GDPR will be interesting in the fediverse as once it’s out there it is really hard to remove/redact on all the other servers that the post has been federated with. It is a problem akin to sending an email to a mailing list and then asking everyone on that mailing list to delete that email… and forward that deletion request on to anyone they forwarded your email to and ask them nicely to do the same.