* Libraries are physical spaces linked to one geographical community.
* Libraries have a limited number of physical copies to lend out.
* To read the books in the library, you have to physically go there, check it out, and take it home (or read it there).
Compare and contrast with a web site linking potential lenders/borrowers:
* Geography is not much of a limit.
* Ebook copies (limiting the discussion to Kindle) are managed by Amazon, but are only scarce artificially - in their 'natural' form, ebooks are not a scarce resource.
* Clicking on a web site to get a book is far, far easier, quicker and more convenient than going to a library.
That's just off the top of my head. Presumably, if you were not being willfully obtuse, you could think of a few differences too.
I don't understand how anyone can hope to discuss this stuff in a rational way if they're not going to look at the facts as they are.