I love the style of analysis, but it doesn’t hit on some key things, imho.

1. Japan pretty much missed the desktop internet phase in the 90s and early 00s. Services like Compuserve and AOL (or Japanese equivalents) were not often utilized. ISPs, while often quite good (shout out to TWICS), were used mostly by tech folks, who have never been in high demand or had high prestige in Japan. A consequence of this is that desktop-based web design in Japan did not have a robust or competitive forcing function for optimization or usability in the 90s or the 00s, and then was just able to be skipped by the smart phone revolution.

2. That said, and as mentioned by the OP, Japan was way ahead in cell phone tech. In the early to mid 00s, I used the web as a critical info dump for some folks with whom I was working. They all accessed via phone, and I quickly learned that I needed to design accordingly (light and clean) if I wanted the info to be accessed and used. Most commercial websites were not designed this way, and they also were not accessed by users regularly — the data charges would have been insane.

3. Class signals 1 - I read something about minimalist design in Japan many years ago that jibes with my anecdotal experiences. Basically, if you see something with a simple and clean design with a lot of empty space, it’s usually a signal of high class and/or high quality and almost certainly high cost. This holds for a wide range of things like magazines, restaurants, menus, hotels, etc. Most Japanese folks see these types of designs as either expensive things to avoid (due to budget) and/or possible conspicuous displays of affluence that are frequently avoided by those who have the means (there are some folks who like to virtue signal while pretending to be something that they are not, but that’s a different issue). So a default reaction for many Japanese people to an empty design, especially empty dark, would be “I am not their target market”, even if they actually are.

2. Class signals 2 - The following is my opinion based on my experiences living in Japan for 8 years and working with things Japanese for many more, and I have no citations, but… Japanese people across the whole country (i.e., not just people in Tokyo) can mostly be grouped into the category of middle class income with working class tastes. This can be seen across a wide range of categories including food, clothing, housing, media consumption, etc. The exceptions outside of this large group (e.g., people who were raised with and embrace a classical and traditional upbringing) are easily noticed once some amount of time is spent with them.

As a simple example, compare the design of this sports newspaper (https://en.m.wikipedia.org/wiki/Sports_Hochi) with that of its mainstream parent company counterpart (https://en.m.wikipedia.org/wiki/Yomiuri_Shimbun). The “everyday man” magazines and newspapers with the bold and garish design are abundant and ubiquitous (easily seen in convenience stores), while the relatively gray and conservative mainstream paper is pretty much only seen in salaryman-world. Japanese websites look quite a bit like the sports newspaper (to my mildly trained eye), and I think websites mimic this design because it works with their target audience. I think that this is comparable to sites in the US that lean heavily on ad networks like Taboola and Outbrain as their primary revenue sources — it works for their target market.

CONCLUSION

Internet use in Japan has always been an enigma to me. Japan has been so far ahead in some ways (e.g., I had screaming fast fiber optic to the home for less than $100 a month in the mid-00s), while being so far behind in so many other areas.

I think that there is a lot of room for disruption for companies that can take the reality of Japanese web use and tailor a better design around that reality. It seems like there is a lot of design inertia that is very sub-optimal. I’m not sure if the best way to attack this is by segmenting aggressively and targeting a lot of small accessible markets, or if the only way to changes things will be via a big mover that dictates online design taste (e.g., a domestic, Japan-grown Apple type of company). Perhaps both are possible.

Anyway, I hope that others who actually live and work in Japan can add some additional insights to my comments.