(I'm wondering if you think the objection is to scrolling, it's not, there is a difference between a long page with scroll bars that give an indication on how far you are on the page, and infinite scrolling where the page gets longer each time you read the end of the page)
From dictionary, book: "a written or printed work consisting of pages glued or sewn together along one side and bound in covers."
if there were a single piece of paper long enough to hold the entirety of a book, and it were written out on that page, would that make it any less of a book? it may not be one in the sense that it is no longer bound together, but at the same time, in the former example the pages were bound together by some chemical process into one monolithic page; the only thing missing is a cover to hold it together, though I have seen college textbooks come as just loose leaf paper that one has to bind themselves but that's still a "book" prior to binding.
also: what if a story or some such were to be written on a scroll? just because it doesn't fit the precise literal definition of what a book is, doesn't mean it doesn't contain the same semiotic substance as "book" and as such doesn't mean that it automatically isn't one. but maybe im just being pedantic ¯\_(ツ)_/¯
Honestly scrolling on mobile gets me halfway to a repetitive stress injury, I’ll take a next button anyday