[suslik]

While accurate, it isn't a full answer. Substack does provide profits for venture capitalists, but it does so by fulfilling a particular market demand - demand for a censorhsip-free (or censorship-lite) platform. It is a somewhat niche demand, obviously - but it is the only aspect that differentiates them from facebooks of the world.

[throwawaygh]

No, it is the full answer. The other stuff is their market position. That can change on a dime. (It also does nothing about to dual problem of stoking social division to generate more profit.)