As someone who has looked into this quite a bit it's not difficult to do what Google Books had been doing in 2017. The reason is that various groups have ripped and converted to PDF thousands of books. It's trivial to facilitate search on these and other cool stuff at this point. Someone could do it if they really wanted too without too much effort. They haven't most likely because there isn't much profit in it as it stands and legal hurdles since Google failed.