Well they have to destroy them after scanning, else it is a copyright violation. Maybe not in the US, but in a lot of jurisdictions you are allowed to make copies/scans of Books, CDs etc. but if you sell the media, you have to delete the copy.
Given that anthropic was just fined a $1bn fee for torrenting/piracy, we cant really blame the companies for shredding the books after a scan. We should blame copyright laws.