They are buying physically rare books from antiquarians with online listings. Those books are all out of print, or they'd just buy a new copy that's readily available and surely cheaper. Rights are irrelevant because the entire point is to create a digital backup copy... in accordance with copyright law.
It'd be great if they could toss these scans onto the Internet Archive. But they can't. Legally that's the same as piracy, which is the whole reason they're doing this, instead of just mirroring Anna's Archive. That was their first whack and people were aghast. Funny how they're not any happier, now that these companies are doing things "the right way."