I have lost count of the number of HN posts questioning why Company X "should" need anything more than Y number of staff. If all it took was the tech stack, then everybody would be on ConvertKit or MailChimp or Tinyletter, companies with a long track record.
And yet, within months of is announcement, Substack is better known than any of those other tools. They are paying six-figure advances to shore up their portfolio of writers. And, like all VC-backed startups, they are spending massively on Google and Facebook ads.
Building name recognition that quickly isn't cheap.