For readers who aren't subscribed to Medium, it can be annoying. You go to read an article, and if that article is monetized, you see a banner to sign up. Plenty of people leave immediately.
Now let me tell why, as a writer, I still use Medium and will continue for the time being.
I only post 2-4 articles on there per month. But even then, I'm seeing ~50K views per month and this month I'm on track to earn $1000.
To see those same results on my own blog, I would need to learn a lot about SEO, affiliate marketing, and have a large Twitter following to direct traffic to my blog. I would also need to maintain it myself.
Sure, I might have a higher chance of going viral on HN, but how likely is that even anyway?
As a full-time developer with a newborn who's just looking to earn some fun money, Medium is perfect. I write, submit to a publication, and they take care of the rest.
People may say, "I'm not going to read your posts on Medium." My answer is: okay? Can't make everyone happy. But I'm still getting 50K views from people who do want to read them, and I'm okay with that.
The other point to make is that Medium only pays for views/reads from other Medium members, so I don't necessarily care if I go viral on HN or not. If I really cared about going viral, I would just post my article to something like dev.to and then submit it to HN.
If you're just looking to write and get views/go viral and don't care about money, then it might not make sense to post to Medium. But if you want to earn some money with relatively little effort, Medium is hard to beat.
Edit: Here's proof of my claims for people questioning them (https://medium.com/@SunnyB/proof-of-medium-stats-700c2b0b638...). Note: it is a Medium link to an unlisted post. Didn't know where else to put it.