It can be done in a way where it's not transparent to all parties. Blockchain wasn't designed for identity. Blockchain was designed for accounts to exchange value. Identity requires privacy. I think sure if Steem wants to only be pseudo anon then this will not matter but if Steem wants real identity and not bots or shill accounts then there has to be some privacy.
Restricting who can access what is the whole point of privacy. A blockchain will not reveal much if you use blind signatures and other techniques. Voting which isn't confidential is coerced. So Steem voters who use their real identity will be open to coercion. It is even possible some Steem Power holders could be forced by threat to upvote certain accounts.
How can you know every upvote is honest, legit, without coercion? It could be happening.