Mass sharing a scanned book, particularly one that was not OCRed, indeed usually takes too much work. EBooks, or rather most of them, are tiny epub files with little to no images, 5mb maximum. There are sources distributing ebooks at scale, libgen.io is a prime example, the ebooks channel on IRC highway and myanonamouse, a private ebook and audiobook torrent tracker that some people apparently use also exist. There are rumours of private collections spanning millions of titles that fit on a single, albeit large, hard drive.
Gotcha -- an epub/mobi of a novel is tiny and easy to host. I was thinking of more design-heavy books with figures and images, which tend to be much larger.
Still, if people torrent audiobooks (and they do), then eBooks, even with figures, can't be that bad. I've seen hosted collections of audiobooks ranging in the gigabytes and they were not best sellers. No reason why you couldn't do that for ebooks.
