There are a lot of top-to-bottom languages in Asia. Some chinese languages for example are traditionally written top to bottom.
Bidirectional text only really occurs when mixing languages, like in the example above where RTL Hebrew is mixed with LTR English (or in this case specifically LTR file paths that have originally been created in the context of an LTR language and thus are LTR).
If there was actual TTB language support in Windows Explorer, and you had a file path incorporating both TTB file names and LTR file endings and drive letters, then you’d also have the same issue with mixing LTR and RTL, only that you are now mixing writing directions in two dimensions.
But I’m guessing even though Unicode’s stated goal is to encode all writing, TTB is probably where they drew the line.
It is. Did they just rotate the page after rendering?