I've sort of thought that part of the reason earnings have fallen off is the number of writers trying to make money on Medium may be increasing faster than the number of people paying for Medium subscriptions. When you have more people taking a slice of that $5, each one gets less, especially when a lot of subscriptions are still affiliate subscriptions so 50% off the top goes to the affiliate.
That said, I do miss the months where I could make several hundred dollars off of Medium. But I've never counted on Medium for more than paying for my Medium subscription and, on a good month, my Adobe Stock Photo subscription.