In printed text you would mostly have seen a single font used on a page, if not for the whole work. There's no inconsistency when there's a single font, especia

In printed text you would mostly have seen a single font used on a page, if not for the whole work. There's no inconsistency when there's a single font, especially not when the only variations are the odd piece of italics, a few (pretty much pre-defined) styles for headings, footnotes etc. and no zoom or different display devices. If you could turn a paperback sideways and have the text flip it would look pretty bad - lots of the layout and text is either hard-coded or even manually applied based on the physical format.