I've noticed the same thing. Other articles can do well, but it's rare.

I think Medium and writing topics often do the best because writers can easily relate to those subjects. Everything else is going to be more of a niche.

However, a very small group of writers get massive reads writing about other topics and I still have no idea how that happens.

It's almost like the Medium algorithm treats some writers differently in relation to the distribution, but that's my theory with no data to back it up.