Maybe I should've said a "screen" instead of a "page" (if you have two files open side-by-side and they both fit on your screen it's the same benefit). And I admit it is slightly hyperbolic (to make a point about the virtues of being able to see a significant portion of your project at once). Large projects will be more than one screen of code, although perhaps surprisingly few. (This actually influences how I organize code, in that the "screen" becomes a logical unit, and I try to keep the API surface of each screen really small.) I'm working on a programming language project to try to get even denser.

>Good luck fitting an operating system, web browser or air traffic control system into a page of code.

Aaron Hsu's co-dfns compiler (optimizing compiler for a subset of APL to the GPU) is 3 screens https://github.com/Co-dfns/Co-dfns/tree/master/cmp (I can fit the entire codebase on my three monitors).

This K text editor is way less than one screen https://kparc.com/edit.k (Funny you should mention OS. I'm eager to see how many pages kOS is. AW notoriously hates scrolling.)

Web browsers are a lost cause, I'll give you that one.