Print media evolved into its present forms.
In, say, 1469, there were no page numbers. This obvious and now necessary part of the book's user interface simply did not exist.
The earliest extant example of sequential numbering in a book (this time of 'leaves' rather than pages, per se) is the document you see at the top of this page, Sermo in festo praesentationis beatissimae Mariae virginis, which was printed in Cologne in 1470. The practice didn't become standard, the wonderful I Love Typography tells us, for another half century.
The page number is particularly interesting, I think, because it is a pointer, a kind of metadata that breaks apart a work into constituent parts. The existence of page numbers creates a set of miniature sub-publications to which someone can refer.
Now, books can be sliced and diced in an ever-expanding number of ways by computers. In a recent book I read in the Kindle app on my phone, a highlight I made came at location 7525. There were 8958 possible locations. These are really the page numbers of the e-book age. We're still living with the coarse resolution that the print formats provided, but that's changing.
Google Books is carrying on the tradition of this 15th century German printer, too. The precision of its pointers has extended down to any individual word or sentence, as well as strings of phrases held together by search engine code.