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.
Oh whoops, I deleted my comment almost immediately but it seems like you could see it and answer anyway. Yeah makes sense that it’s not an all-instances thing, it was very weird UI-wise because it said “optional” but then the address still came back when I left it empty, saved and refreshed. Seems like they might have forgotten to remove the “optional” label (or remove the requirement, either of the two).