I myself am much more interested in the data behind the people in the process of going from 0 to successful, even if they fail; not the hindsight blog posts about people who are already successful.
I understand that sentiment and have no argument against it, but there are tons of stories posted to HN with similar attributes (single founder SaaS, $3-5k MRR, blog post likely submitted as a marketing tactic) and none of those blow up the way this has.
To try and answer that question, I think its because this one is fairly easy to read, understand, they're very open with their data, they show their work on how they calculated MRR (which is probably useful for some people), and while yeah this is probably a marketing tactic, they are also not really being pushy about it.