On kbin, everything is sorted by magazine. users don't have a personal "microblog", every time you make a microblog post here on kbin you're forced to pick a magazine (you can pick /m/random if you don't want to pick).
Like, I can't understand a use case where it wouldn't be preferable to just use articles.
That's because you're looking at it from the kbin perspective. You need to understand that the microblog posts came first, and are there because of platforms like mastodon that work to recreate the twitter style experience where you follow users and see their posts, and posts aren't sorted per "subreddit" or "topic" but rather by user, and searchable with hashtags.
Lemmy then came along and created this threadded reddit-style interface, forcing every post into a "community". These are basically the exact same thing as the older microblog posts, but with an added community to categorize it.
Kbin came out after that, adding support for lemmy-style threads, and mastodon-style microblog posts. To handle mastodon stuff, each one is automatically assigned a magazine to help categorize it into the familiar magazine/community setup; even though they aren't sorted like that to mastodon users.
As kbin users we can choose whether we want to create a thread or to create a microblog posts. They have a difference nuance to them. Threads have this expectation of being a part of a magazine/community, like a subreddit, with the expectation that people in that group will see it. microblogs have the expectation that only the people following the person who posted it will see it, not everyone subscribed to a particular topic. this means microblog posts are often a lot more personal, more informal, less "professional", and not directed at a community.
If you create threads like you'd use reddit, and microblog posts like you'd use twitter, then you've got the right gist I think.
Do Twitter or Mastodon have some analogous feature where one can have a named microblog independent of one's personal microblog?
No. To mastodon users they don't see our magazines at all, whatsoever. They just see it as if someone tweeted out the thing without any actual categorization.
tal