it's just a blogging platform + newsletter service. There was never an expectation ppl would make a living income from it, except for only the top. But it's like this with almost everything in life.

Yes there was. The monetization was why it wasn't medium.com. Friend of a friend is a substack writer. 50k subscribers that pay $10/month for her insights.

I said "except for only the top." With 50k subscribers, presumably this is in the top tier

Why do they host it on there then, can't they just get a domain and own their data/content?

It's a blogging platform built around an app , which is like a quasi-social network in its own right.

Some short answers are ease and discoverability. I use Blogger myself after fiddling around some mostly because it was easier (and a bit cheaper) than setting up and hosting something myself.

>except for only the top. But it's like this with almost everything in life.

For creatives, however you care to define the term, probably. But there are a lot of professions where fairly run of the mill professionals and even tradespeople still make a pretty decent living even if they're not partners in their organizations or own their own businesses. Of course, you get down to the tier that's doing taxes at Walmart or working in an auto parts stoor, not so much, although probably still more reliable income than the average Substack writer.