My list of reasons Medium failed. - Their in-site discovery sucked. Like many users I would discovered Medium articles via external networks, but once on the site, I never found their "similar articles" feature to give my anything worthwhile. Also their editorialized recommendations seemed to have a hidden social-political agenda. But what media platform doesn't? - Most of the content had quality barely above a tweet…
Honestly, I was/am quite the opposite kind of person: I mostly went to Medium for this kind of long reads. When the articles typically became shorter, I became much less interested in reading them - as you described:
> Turns out you can't say much in 10 minutes that wouldn't be a better Tweet. This lead to a race to the bottom in terms of article quality and length.