Google didn't buy the books they incorporated into books.google.com either.
You can use books without buying them. e.g. libraries, or borrowing books from anyone even if they're not a "library".
Copyright is not about internal use, it's about copying and distribution.
This is not about what anyone thinks should be legal, but rather what is legal under the current law. The law was not designed for the digital era where "use" could be something other than a person consuming the content, and this has not been meaningfully addressed, therefore other uses are legal by default because that's how the law works.
You can use books without buying them. e.g. libraries, or borrowing books from anyone even if they're not a "library".
Copyright is not about internal use, it's about copying and distribution.
This is not about what anyone thinks should be legal, but rather what is legal under the current law. The law was not designed for the digital era where "use" could be something other than a person consuming the content, and this has not been meaningfully addressed, therefore other uses are legal by default because that's how the law works.