Interesting questions, Bridget. I believe that Medium is actively driving the dominance of certain writers because they provide the content Medium wants. Money is tied to that decision to be sure. The more Medium earns (including new memberships) the more the algorithm drives traffic.
Their content generates conflict, disagreement, and protests, - all of which increase readership.
Imagine the Rose Bowl filled with writers trying to be heard. Then suddenly a very bright spotlight is directed at a section of 100 writers. Everyone's attention turns to them and they are heard above all others. That's what Medium is doing. Writer better, use social media, edit your work, and write more often, all of these statements have a little truth attached to them - but that's not why many writers aren't being read. AI is directing the readers elsewhere.
Walk into any store and look at the displays. Those that are front and center, colorful, and can't be missed - someone is directing your attention to them first and foremost. It's intentional. Cheers.