I think there are some important points missing.
Japanese society can adopt things fast the "keitai denwa" where created and adopted earlier than anywhere in the world but in 2025 most companies still use fax machines. The japanese society seems to have different citeria for adoption and depreciation of technology (compared to the west).
When considering web layout you have to consider traditional media layout for example magazines, newspapers, books, flyers or comics. With the japanese language it is possible to layout your articles (text) in different directions left-to-right, top-to-bottom and top-to-bottom, right-to-left. Magazines are read from (western)back to front. Basically there is more flexibility in layout compared to other languages but translating that tradition to the web is difficult today and historically was very difficult.
Most visited websites are news pages, those will be layed out more similar to a traditional newspaper. In japan they often adopted a column layout where in the west we adopted a more list like (row layout) format.
As stated in the article CJK characters are problematic, however the japanese text especially is confusing (because they tried to solve it early on) on the encoding side as there are a few standards that don't cooperate. Especially on the early internet due to technical limitations and a fractured technology landscape (different devices, and operating systems).
Therefore a lot of websites that wanted more advanced layouts opted for (and still do) publishing images embedded in html for more advanced font and layouts.
Also most japanese primarily visit japanese language text websites and therefore don't come in contact with the western website design styles very often. A lot of non English speaking countries have this however in japan it is common because of the relative cultural separation. Most japanese just don't interact with companies people or media outside of japan often, a huge part of this is because they are a first world country that has a very low English proficiency. leading to the two styles evolving independently.