Why are the companies legally required to shred the books? That's the most surprising part about this to me. Surely if they bought them second hand they could donate or resell after scanning. I'm wondering if the scanning machines are damaging the books.

You're not allowed to make copies of copyrighted work. Of course this law was made long before the reality of digital books.

The argument for the digital era is that you can make a digital scan and it's not a 'copy' so long as you shred the original and don't attempt to distribute it.

The legal idea behind it is that if you "copy" the book it's bad because now there are two copies and you "stole" from the author, but if you "move" the book to a digital form (and don't copy that outside of your organization), it's fine.

Given that they have to destroy them anyway, they're obviously also going to use the much cheaper destructive scanning (cutting off the spine and using a feed scanner rather than carefully turning page by page).