The problems with much of the audience is not that they do monetization, but how they do it.
Like many readers, I don't read enough Medium articles to pay $5/mo for it. I don't mind paying $5/mo for something useful, or sending a one-time donation. I gladly would pay, say, 25-50¢ for a good article, if I could do it without subscription. Such a commitment just feels unnecessary.
One way to do it is ads — good thing Medium is not pushing ads at me! My thanks. But there's still no easy way to pay a small amount.
I see how microtransactions are not economical. I wish Medium offered a "casual reader" plan, where I post, say, $10, and they go to pay per-article fees, not limited by time, that is, I'd not need to replenish it monthly if I haven't run into zero balance. This could be a gateway for more readers who just don't see the need to commit to a subscription. It could even lead to more conversions to subscribers.