I live in Japan and personally I think it's cultural and has more to do with the aversion to change and also the critical shortage of competent IT professionals and foreign-language speakers in this country. Often times websites aren't just designed differently, they are lacking basic functionality. Any foreign resident has a story about how some important website like their bank or a government site wouldn't let them in because their name was too many characters to enter into a text field or something. The government released this contact tracing app for covid and it didn't come out until like 5 months later that the app was broken on android and just literally didn't do anything. Japan's former cyber-security minister was outed as having never used a computer in his life after admitting in front of some committee that he didn't know what a USB drive is. Just look at the difference between Amazon jp and the local version, Rakuten, and it's clear how dated and non-functional Japanese sites are.
The problem is these companies are all headed by septuagenarian nepotism hires who can never be told they're wrong, staffed by programmers who have no idea of industry best-practices because they've been trained by these old guys who don't have a clue either and just want to keep doing what they've been doing since they learned to code in the 90s and can't read non-Japanese documentation, and the consumers also are tech illiterate enough not to notice or care that the websites are dogshit because they're used to it and again never access any non-japanese content because of no foreign language skills. And also old tech is rampant in major companies for the same reasons, which means often times these ancient devices are too slow to run modern websites well.