If I have to be honest I don't see much from this either, but a potential upside is structural separation of text and presentation in a way that's different from HTML/CSS, in this case the content would be pure ASCII text as opposed to a tree structure/object model.

I'm not sure I agree with this premise either, the hierarchical structure seems inherently semantical to me, but the argument of the OP is it isn't the case.

> what's the point of making it a text format at all?

The text part is ASCII, so it make sense to represent it as such. The "presentation" part could be binary.