They want to be "good citizens" in the book-publishing ecosystem. They follow along with the publishers' schemes, to ensure that the channel for public access

They want to be "good citizens" in the book-publishing ecosystem. They follow along with the publishers' schemes, to ensure that the channel for public access to the material remains open. They don't want to risk the possibility that there might be knowledge out there that an ordinary person might be barred from accessing via the public library. And as long as the publishers are reasonable, even when charging a higher library price, that's cheaper than libraries setting up a different infrastructure. The mission of most libraries is about access and public service, rather than raw price. The publishers can abuse that.