One big difference. Substack is push, blogs are pull.

Managing the reliable sending of millions of subscriber emails is expensive.

How much?

Mailchimp charges $12K/year for 150K contacts and 180 emails/contact/year.

(Above that is "call us" pricing.)

At that rate, it is about 10c per contact per year. Substack has 500K paying reader-subscribers, 10-20x that in "total readership", whatever that means, and "millions" of readers (but I believe those are web viewers).

https://backlinko.com/substack-users#how-many-paying-subscri...

I would guess mostly marketing—building the brand and the audience. Also recruiting writers to the platform.

You pay writers to come to your site and all the other marketing gumph.