The main thing is that no one wants the hassle of keeping up with 50 mildly-interesting blogs by visiting them regularly. You really need a "push" mechanism of some sort. Social media doesn't work for this because if someone subscribes to a content creator on X / Twitter, they most likely won't see most of the creator's posts. Instead, the algorithm will show them cat memes and other on-platform engagement bait.

Many other social venues are gone too. If you're lucky, you can reach your audience on HN, but it's about the only remaining, successful aggregator of this type. Reddit has grown a lot more insular and many subreddits don't allow outgoing links. Where else do you go?

In this reality, the most practical push mechanism is email, but sending email to thousands of recipients is hard. You pretty much need to pay someone for the privilege if you want to have a reasonable success rate. Substack will do it for you for free, and it also lowers the friction because it gives visitors a familiar UI with a pre-filled address and no concern about phishing / spam / etc.

Beyond that, I don't think Substack is actually that much of a community. They built a good brand by attracting (buying) a bunch of high profile writers, then had an issue with neo-Nazis where they took controversial stances... I don't associate the domain with anything especially good or bad, not different from blogspot.com or wordpress.com. I have a special hatred for medium.com because almost everything over there is aggressively paywalled, but that's another story.

And yeah yeah, RSS, but the friction for RSS is much higher.