HN seems to have no idea how bad it is in the journalism field right now, so here's real facts. A lot of Substack's poularity is journalism, with some major writers for fun (e.g. I follow Chuck Palanniuk's Substack).
TLDR - First off yeah employees are posting here duh. But HN people want writers/journalism, and Substack is "getting paid to write". Or, it's Patreon before Patreon started blatantly censoring views they disagreed with politically. But I'm not even blaming Patreon per se, I mean larger world forces cutting off many forms of expression. If you haven't followed, look up how the United States government has attempted to freeze the porn industry from being able to accept credit cards or keep bank accounts (including the Obama admin just so you know the left does it too).
Credentials: Divorced from a journalism major who turned advertising and works c-level of an international company. I work as a programmer in ecommerce where I work very closely with marketers, and have seen this experience repeated.
Journalism is about as useful of a degree as Gender Studies, which given the political undertones is a good comparison as there is a ton of crossover. Journalism as a field - in America, across most types of employment - is an insanely incestuous clique of mostly liberal East Coast elitists. I mean that very literally, as in people who think either Boston or New York City are the be-all end-all of the world and how could you possibly live anywhere else. (well, pre-pandemic.)
So my ex went to an Elite East Coast College. What happens after you rack up five or six figures of student debt is that you go to a Mad Men sweatshop. Some sort of agency generating copy for newspapers or ads or whatever. You're worked 80+ hours a week for minimum-ish wage (certainly too little given the stress). You'll walk into work and get told you need to crank out something absolutely absurd. Just for fun let's say it's 20 articles of 800 words by end of day for a field you've never even written before so you don't even know the jargon. So you may end up working from 8am to 11pm, and only being paid crap wages for 8 hours that day because it's not their fault you can't make quota. You're just madly copying and pasting garbage to make requirements and hit SEO targets. That's how vast amounts of the Internet is generated. All the mommy blogs and recipe sites that seem like a word salad. "Recipe for Chocolate Chip Cookies. I recall fondly my mother used to make chocolate chip cookies..." (page length requirements, reader time on site requirements, keywords...)
So you racked up near to six figures of debt, as far as you're concerned a 40-hour week for fair pay is a myth capitalists make up to torture you, and you've spent the first 20-ish years of your life building up little more than a damaged liver.
So who's left in journalism? AKA who can Substack target?
0) Bright-eyed college kids who don't know any better. Keep in mind that if someone tells them they'd make more money at Substack, then Buzzfeed calls that an "alt-right dogwhistle" from a "controversial figure" to keep the peons in line. When a Buzzfeed goes bust as their employees finally figure out the Ponzi scheme, they all end up on other platforms anyway. No need to invest here.
1) True die-hards who stuck with it, which I'd say is people like Matt Taibbi and Glenn Greenewald. You'll notice both of these people are in hot water with the political left for various offenses, and are desperately looking for a better revenue model to keep journalism alive. Substack does that for them, like Patreon but less censorship. As people posted - they're helping censored Russians of all walks of life to be able to publish after sites like Patreon have axed those people because mumble mumble oligarchs? True free speech stuff, even if you disagree with their other views, these people are net positives on the world. They're already hungry for Substack.
2) People who have other funding, like the marketers, who were probably paid to join. People like Chuck Palahniuk didn't really need Substack, but it's hot, and it's like Patreon except he presumably gets a better kickback. So why not. I know comparitively few people in this camp unless it's terribly obvious they had the following to get paid.
So Substack did the right thing in every regard. The site gets people paid, it's fairly easy to use. They went after category 1, they paid off some people in 2, and I'm sure they keep an ear to the ground and drop some timely social media posts when a 0 event happens. And yeah, look around. They're posting right here, right now, where it's effective.
They're the right tool, at the right time.