The screen is infinite but information should still be prioritized, that is why newspapers use different sizes of headings. If they truly wanted to jam everything in there, they'd use the same small font size and save on paper, but that's not what people like because they want to see at a glance what is important and what's not, and that's done by the font size initially. This is no different on an infinite screen, the design principle of information prioritization still holds.