Coda is a knowledge base, much like wikis such as Confluence. It's mostly used inside businesses, so I imagine he just made this page public. Making it hyper optimised for anonymous web traffic is almost certainly a non-goal.
I am suggesting that if you want to blog, and want people to read what you blog, to host it somewhere where it is readable on the widest range of devices. If a iPhone 6 with a 20Mbps mobile connection is too antiquated to render the site, then they are probably cutting out a lot of audience.
I don't know Coda, so I'll use the Confluence (which you suggest is similar) as an example. If I am using Confluence it is because I have to, for work. I will make a provision that maybe I can't read it on mobile and I need to be at my desktop. If I am reading a blog post from hacker news, I probably wont go to the effort of bookmarking it later to read on a desktop PC.