The way the laws are written, you have the right to digitize books that you own physical copies of. If your physical copy is destroyed, you retain ownership of the digital copy. But the moment you transfer ownership of the physical copy to someone else, you no longer have the right to your digital copy.
You're asking how it's legal for them to remove books from circulation, when that's the only way under the current laws for them to obtain permanent digital copies, legally.
You're asking how it's legal for them to remove books from circulation, when that's the only way under the current laws for them to obtain permanent digital copies, legally.