You're severely misunderstanding a lot here. Interactions with other users are by no means limited on itch just because they're public, and they're a large part of the way many people use the site. The discussion posts feature exists for a reason. Your malformed personal opinions on private messaging really have nothing to do with whether or not itch can be considered a social platform when it's very frequently used as one.
There isn't a distinction between "users" and "developers" on itch, so I'm sincerely having trouble following the second paragraph. Uploading an .exe file doesn't bar users from leaving comments or opening discussion posts. Banning someone from a game's page isn't an answer to being antagonized in different areas of the site.
There's also just the simple fact that there are reasons to block someone that wouldn't necessarily get them banned. You can be harassed or stalked off-site. Someone can poke and prod at you in a way that doesn't overtly violate any terms of use but is clearly meant to hurt you. Hell, people can just get on your nerves. That's all enough to stop or at least hide their interactions with you. Just letting the site's moderation take care of it isn't a solution to the problems this post is actually raising.