I started publishing my articles, newsletters, and podcast on Substack about 2 1/2 years ago when I noticed my Medium views and monetization were dropping.
I decided that I didn't want my content to be held hostage by Medium's algorithm, which apparently decided that only a fraction of my followers should see my new articles. I love owning my audience on Substack and knowing they get my emails straight into their inbox. The built-in podcast hosting is so easy and is the only reason I started podcasting every week.
The big bonus is that your email list is portable. I have my list in ConvertKit as well. I'm no longer beholden to one platform that puts a barrier between me and my audience. They can come with me wherever I decide to go and host my writing next.