The technology argument is the most convincing one to me. I worked with a Japanese client a few years ago and the internal tools they used were wild by western standards. Like full-on frameset layouts in 2020. But it wasn't ignorance, it was continuity. The tools worked, people knew how to use them, and there was zero appetite for redesigning something that wasn't broken.
The font thing is also underrated as a factor. When you only have a handful of web-safe CJK fonts and you can't rely on weight/size variations to create hierarchy the way you can with Latin text, you compensate with color and density. It's a constraint that pushes you toward a specific aesthetic whether you want it or not.
I think the framing of "peculiar" is a bit western-centric though. Dense information-heavy pages are arguably more respectful of the user's time than the trend of spreading three sentences across five viewport-heights of whitespace.