My comment was regarding reCAPTCHA not being used to convert scanned book pages to text.
For books older than my mom, most of which must be public domain, there are a lot online archives. In fact, some of the more common archives like Project Gutenberg, are available as free ebooks on Kindle and iBooks. For more obscure titles, there are field-specific archives from where Google accessed them.
They only got information from publishers and archives. So information you're looking for is out there somewhere in digital form.
The difficult period is approximately between the 1920s and 1990s, where books are under copyright and may have become orphan works (rightsholders cannot be found).
How old is your mom that a book written when she was alive is almost certain to have been written by someone who has now been dead for more than 70 years?
Were that true, you'd think Google would be able to find it.
> Were that true, you'd think Google would be able to find it.
Or not - because of copyright laws. :-(
Project Gutenberg was a thing before Google Books, and those two things aren't the only source of electronic versions of books "older than your mom", or even the only source of free electronic versions, where such isn't legally prohibited by a combination of copyright law and preference of the copyright holder.
Perhaps for kids looking for new books that's wonderful, but those of us that use books older than your mom, there are no ebooks. Google Books was literally the only place to access that information outside of a few select world-class university libraries.