I think this is a common misunderstanding. The images are in the public domain. Nothing stops Getty (or you, or anyone) from selling them, even though you can just use them for free.

The value-add service that Getty offers is legal indemnification, i.e. they cover the legal costs if the image turns out to be copyrighted after all. To offer this service they spend some time and money upfront to research images' copyright status.

Whether you think that's good value for money is up to you.