I ask: why?
Because, they reply, it's easier to print. I also suspect an answer is: because it's easier to copy. I've never heard any argument that doing so would improve learning.
I have no interest in making the information on my sites easier to print. My essays are designed to be read online and take advantage of that environment. This includes ancillary tools such as sound files to help with pronunciation and images like maps that help with understanding, or even just pictures to help with visualization. While the images can be printed, they are never as clear, and in any case you can't zoom them; sound files, of course, don't exist on paper.
I actively discourage such habits as highlighting, which is how some students think studying happens, so that's another reason not to facilitate print.
I do suspect students, especially public school students, of copy/pasting entire passages. It's a near certainty. Putting everything in one file merely makes that job easier, and I have interest in doing that. Beyond that, however, I know for a fact that other sites duplicate my content without permission, and I want to make that task difficult for them as well.
Finally, there's an issue of scope here. If it makes sense to put all the pages of an essay into a single file, why stop there? Why not all the essays in the entire site into a single file? Heck, why not all my classes, just one great long file? On the contrary, if anything, I'm moving towards increasing the granularity of the information.
Are there any benefits to my approach? Well of course there are.
First is readability. I don't try to keep "above the fold" but I do try to keep pages relatively short. Within that very vague guideline, I try to make each page self-contained; in fact, my model comes from the very old-fashioned style of history books that would have inserted headings--not chapter titles nor even section headings, but indicators of a change in topic. Typically these would encompass only two or three paragraphs. I try to break each page at a logical point that would propel the reader on to the next page. Readability is, in other words, a consideration both in terms of screen reading but also in the rhythm of reading.
Second is ease of reference. Discussion is important in my pedagogy and by breaking an essay into many pages I facilitate references, both in discussion and in papers.
Third is findability. Search engines are happiest when each page is about a topic. By breaking an essay into many pages I can title each specifically and adjust keywords as needed.
Finally is performance. Because I make extensive use of media, an entire essay in a single file would actually be pretty hefty, even by modern standards. I try always to be cognizant that my work is on a world stage, so I try to keep the footprint of any single page as light as possible.