It's a content container. A content container that for some of us is now stereotyped as "content in here is often low-quality", which means that in the vast amount of content on offer each day we're more likely to skip links leading to medium.com. If people regularly spread bad blogspot links around, blogspot would have the same reputation. (I'm sure there is tons of spam on blogspot, but when people share blogspot links in my circles they usually are blogs by people that have been at it for ages and care more about content than appearances, so for me blogspot is a high-quality signal)

Being in a known content container is great if you don't have your own "brand" and as long as people associate the container with good content. If they don't, or if your content is way above average, it pulls you down (which provides motivation for below-average writers to write on them, hiding in the crowd, and motivation for good writers to leave)

It is a centralized content container, which makes click-bait titles like this one better material. So you can create a controversial opinion on a subject, get views, make it an entertaining even if exaggerate read and it gets featured among other pieces especially if you use the right popular tags, then your post is on people's medium app and newsletter subscription.

WordPress, on the other hand, is open source software you can host it yourself and thus you can't just slap some tags on it and get featured on top of a newsletter. This is also why some authors prefer medium, easy to setup and easier to get an audience, but then you have to resort to these marketing techniques to drive your views up.

Disclaimer: I have written some medium posts with catchy/controversial titles to test said techniques, call me part of the problem.