itch is not a social media platform. There is no private message system. So a "blocking" as needed in real social media is not needed. I cannot spam and harrass you privately. And if someone does it publicly, report those people, so their account will be banned.
If you are a publisher, you do can ban accounts from commenting on your game. Also publishers are not allowed to ban users from using itch, so why wonder that blocked users could still buy your stuff? It would not even be valid blocking, because you do not even need an account to buy stuff. And just banning people that downvoted your game to increase your ratings is too easy to exploit.
The point in blocking here is not protecting of privacy, but to filter out stuff that is not bannable, but triggers your shitposting migraines.