And also any time numbers are used in RTL text*, which is pretty common. Besides, you might be surprised how often English words or acronyms are used in everyday texts. If there's a news story covering the American FBI, there's no way to avoid writing it as "FBI", in Latin letters.

There are a lot of top-to-bottom languages in Asia. Some chinese languages for example are traditionally written top to bottom.

But is that how it's rendered by default when typed into a computer, for example into Notepad? Or into a chatting app like WhatsApp, Telegram, Discord, etc.? To my knowledge, they are rendered horizontally unless the software is specifically configured to render them TTB.

But I'm guessing even though Unicode's stated goal is to encode all writing, TTB is probably where they drew the line.

I believe there actually are a few TTB properties in the Unicode database.

* except that one language that also uses RTL digits. I don't remember its name or where it's used, but it exists.