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.
I’m almost willing to bet that big tech companies are already doing this. They got the motive and the means. No doubt Meta or Google have dedicated some of their servers to mining our Lemmy data in this way.
With only around 100k users and most people using anonymous usernames that cannot be connected to their identity it would hardly be worth the effort, time or money.
You’re looking at this from the wrong point of view. The fediverse is not just lemmy: Threads, Tumblr, even BlueSky (albeit with their own protocol, but anyone could just modify their fediverse enabled app to convert their data to be applicable to BlueSky’s protocol) are quickly setting the stage for a new norm. The more websites integrate the fediverse into their stack, the more data outside the immediate sphere of influence of these major corporations can be harvested. To what ends they’ll use it, I don’t know – but I don’t trust them with it.