This is the way I feel, too. I don't think a niche makes perfect sense for Medium, especially if it is not a niche that will ever be curated because it isn't in one of the approved tag topics.

I write about living with disabilities, and those articles are usually my most read stories, but too few people read them.

If I were storing them on a website of my own, I definitely would write exclusively about disabilities there, but Medium's earnings program is not suited to that.