There's a lot of crazy things in the world. Talk to a child about the economy or country borders and you'll realize how some things are just not straightforward to explain the advantages of.
Serverside rendering in JS is no different to SSR in classic frameworks. You generate HTML serverside. Except in this case, you do it using JavaScript, because as it turns out, people develop with JavaScript.
Putting aside how useful it is to only have one language to learn in a stack... Typescript is actually incredible to work with. Working on a typescript and react app is the most productive environment I have ever worked with my past 16 years of programming. The JavaScript world has an immense amount of tooling development behind it it's not even funny.
So when the author says that classic HTML with sprinkled js on top is "easier to develop", I smirk. Developers are flocking en masse towards the SPA model usually BECAUSE it's easier to develop (both with a single language, and in general having the entire app be self-contained). And it's monumentally easier to maintain at scale, too.
EDIT: Clarified that last paragraph.