From what I've seen, much of the earnings issues seem to have started when they removed the multiplier for followers gained off of a story back in August. The earnings from that were merged into the Boost multipliers.

Now, it seems that Boosted stories are the only way to have strong earnings. The multipliers on a single Boosted story can push it to easily earn over $100 on it. At the same time, "viral" stories without the multiplier don't earn close to a Boosted story with similar stats.

With Medium outright stating there has been a huge influx of weak engagement, AI stories to game the system, and mixed with the bot attack at the start of December, it's obvious that there are lots of people/groups trying to take advantage for a quick buck. Like most things, Medium has been reactive to this, not proactive, so some people and groups likely took money away from others who deserve it by shrinking the earnings pool.

I'm hopeful the new changes they're implementing help reward those that deserve it, but we shall see...