The best part of the fediverse is that anyone can run their own server. The downside of this is that anyone can easily create hordes of fake accounts, as I will now demonstrate.
Fighting fake accounts is hard and most implementations do not currently have an effective way of filtering out fake accounts. I’m sure that the developers will step in if this becomes a bigger problem. Until then, remember that votes are just a number.
Federated actions are never truly private, including votes. While it’s inevitable that some people will abuse the vote viewing function to harass people who downvoted them, public votes are useful to identify bot swarms manipulating discussions.