With the pixel density of typical displays these days being as high as they are (phones are often 300-400+ PPI), I think this distinction isn't what it used to be.
It's not just you: Its typography and design is quite unsuitable to reading. The lines are too long, there is not enough leading, the typeface is badly chosen, and the black blocks everywhere are unpleasant and off putting.
Hey, I'm the author of the blog. I agree with your criticisms - I originally designed the website for dark mode users and hadn't really revisited the styling afterwards. I'll be doing some tweaking to increase readability.
"since the result will be not as performant as what they can do with C" -- This isn't the main reason, but it's also not really true. Paradigm changes don't imply "less performance". To the extent programmers believe, herd-like, "C is fast therefore my program will be fast", they are almost always wrong.
A lot of programmers resist learning anything new, for various reasons, but most charitably because they are never exposed to new ideas or paradigms.
The Power of Prolog series is great and what Markus is doing is vital: We must teach that Computer Science is not an exotic, marginal way of approaching software development, but the foundation that we constantly draw upon and inhabit.
I have to admit, though, the New Haas revival is so amazingly good that it makes me want to like Helvetica.