I'm going to give you my assessment.
1. Medium lost a lot of readers for one reason or another. So Medium looked to see where the money was. The money was with 'aspiring writers.' These are the people who want to write for a living. 84% of Americans want to write for a living. I suspect a good portion of them think they're going to be famous. I know that in the days I was a ghostwriter, I lost count of the number of people who wanted me to write their autobiography for nothing, and then they would give me 10% off their takings. I declined. It happens to most professionals. There are a great number of people out there who think they are going to be rich and famous through their writing, so it's very attractive for people 'to learn to write. It's also an enormous market. Consider that. 5% of Americans are regular book readers. 84% of them want to write a book. So Medium switched from being a place for readers to a place for writers.
2. There are a two main reasons why people want to be writers 1. They want to make money. 2. They want affirmation of their worth. Alain de Botton says that the reason so many write is that loneliness has increased tenfold, and that people definitely need to feel connectivity and worth, and having others read one's words fulfil this. This is also where the self-help market comes in - how to do this, how to feel that, how to achieve that. Readers aren't reading because they love reading so much, but because they desperately want to do whatever it takes to feel worth.
3. I was never successful with publications. In the end, I just didn't write the kind of articles that publications wanted - IT, Money, Self-Help, How to write (although I do have a writing publication). I went through your articles. You wrote for some of these., and from what you say, you were successful, and you earned four figures. Like you, I won all four $500, and like you, my takings were 4 figures. And then it changed.
4. It changed, particularly after I was a bit blunt on some comments and people reported me. Medium basically told me if I said anything more, I would be suspended, and so I just lost my appetite for interacting with people, and so my earnings dropped. Fortunately, I have a lot of very loyal readers who read me because they like what I write, and they subscribe directly to me. So while my earnings have dropped on Medium, they have increased on Ko-fi and Patreon.
5. There are still a lot of readers here, and I think Ev Williams was right when he said that people follow writers, not topics. So you must have a lot of loyal readers who love to read you. I would do what some of us are doing - join Ko-fi and Patreon. I have discovered readers to be both kind and generous. Obviously, if your writing was doing well at some point, then it is not the quality of yur writing. It is simply that this is now a writer's platform, and most of the people coming in want to learn how to write.
I wish you the best of luck.