I often find myself asking the same questions. Not sure if this helps, or does anything to answer your rhetorical questions, but I think of Medium as my sandbox, where I get to “play” and experimentally “build” simultaneously. I use it to experiment with different styles, literary techniques, etc. and measure how other readers and writers on the platform respond. If it does well, I reuse what I’ve learned in my other writing. Even if it doesn’t do so well — in terms of likes or stats — but I enjoy the technique or process used, then I reuse that method in my other writing. As a writer, yes I write for readers. But there’s also a part of me that uses it as a cheap version of therapy and an outlet for my semi-nonexistent creativity. Ha!