The website has basically no CSS, so it's up to your user agent to decide on its default presentation.
Just so happens that modern user agents don't really care about bare HTML, just CSS and JavaScript, so your default presentation is optimized to 1990s hardware at 800x600.
I guess "reader mode" is slang for "what the user-agent should be doing to make documents reasonable for modern displays", so press that button in your user-agent.
I'm usually just in reading mode, but occasionally I turn it off to see a/the blogs design because I feel it gives just a little bit more context to any post of text (for example, the author has a playful design and it gives me a small idea of their character). Unfortunate it's hardly readable, but it still says something about the author. HN is fun :)
Haha, yeah, but actually it reminded me of old Web pages. Just text, format it however you want (make the product good yourself!), nothing in the way, just the content.
I'm surprised how much I've gotten used to fancy websites, colors and formatting.
They've put quite a bit of effort into it. That much text is a lot of work.
For what it's worth, their Patreon nets over 3000 / month, so quite a few people think they put in just the right amount of effort, or even above and beyond :)
With Chrome Desktop, and a fairly wide browser window (1475px in my case, required by many web applications), the text is small with minimal margins, and practically illegible. If I shrink the browser width considerably (to a minimum width) then the text does look good, like an ebook.
Asks someone that posts a giant wall of unreadable text.