They’ve also got vote counts and breakdowns of who is making those votes. This data will be worth more for AI training than any similar volume of data other than maybe the contents of Wikipedia. Assuming they didn’t have it set up to delete the vote breakdowns when they archived threads.
Why are those breakdowns worth so much? Because they can be used to build profiles on each voter (including those who only had lurker accounts to vote with), so they can build AIs that know how to speak with the MAGA cult, Republicans who aren’t MAGA, liberals, moderates, centrists, socialists, communists, anarchists. Not only that, they’ll be able to look at how sentiments about various things changed over time with each of these groups, watch people move from one to another as their opinions evolved, see how someone pretends to be a member of whatever group (assuming they voted honestly and posted under their fake persona).
Oh and also, all of that data is available through the fediverse but it’s free to train on to anyone who sets up a server. Which makes me question whether the fediverse is a good thing because even changing federation to opt-in instead of opt-out just covers whether your server accepts data from another. It’s always shared.
Open and private are on opposite sides of a spectrum. You can’t have both, best you can do is settle for something in the middle.