I worked at an energy trading desk some years ago, and market intelligence there came through hyper-focused industry newsletters, with crazy high subscription prices. It's like a Bloomberg terminal, or a Photoshop subscription: only worth subscribing if you are making several multiples of the cost back in profits.

Substack's litany of 'investing' newsletters is basically a mommy blog version of that. Newsletters can't charge very much because we all know this stuff is available elsewhere, in higher quality. And non-financial newsletters probably can't charge at all, other than the small handful you see on their "Featured" page.