Because medium has a better quality level of content and is considered the industry standard blogging platform. While Steemit is more of a niche thing with a very small community. Most people have not heard about it before. While almost every person has probably read a blog post on medium at a certain time in their life.
The economics of Steemit make also no sense. You can earn a lot more with affiliate marketing or even google adsense then people upvoting posts. Because 99% of all the posts on trending page are with bought votes.
The model is not working, the numbers make no sense. So why use Steemit in the first place. Unless you are maybe into crypto or are seeing it more of an investment. Or you simply don't know what you are doing.
Allowing the authors to add their own adsense codes would be nice, while it has to be secure, this would be amazing, I think. :)
At least authors who have powered up like 1000 Steem could get a option by the front-end like Steemit to do so.
My steemit page has 437 followers, but whenever I post something I hardly get any views
Yeah it's a ghost town right now.