[ivanjermakov]

I suspect most of modern Japanese media is horizontal exactly because of a low support for vertical in digital. Multilingual applications and systems rarely favor i18n improvements for a smaller groups of users.

[csande17]

Japan has a pretty strong local tech industry. Microsoft Word needed to add all kinds of features, including both vertical writing and weirder stuff like a dictionary of seasonal greeting phrases to use in formal correspondence (https://learn.microsoft.com/en-us/archive/blogs/office_globa...) to compete successfully with Japanese word processors.

So I suspect the causality is the other way around; there wasn't much demand for vertical form controls for the same reason you don't write emails in cursive.