they ran smack into the common failure mode of building up a large audience and then trying to use that as leverage for user-hostile monetisation tactics.
I was going to say "that's not entirely fair," but I suppose it basically is fair. It's at least worth noting that they still really do seem to be trying to find ways to make it viable for independent writers to get paid for their writing -- their user-hostile monetization tactics are about trying to get you to sign up for that paywall, and that paywall gives a chunk of its revenue to authors who choose to put their stories behind it. The real tragic irony of Medium is that it's quite plausible they've made every poor decision with the best of intentions.