Adding to that, there are obvious logistics involved.

Many libraries won't already have an area to house these books compliant with the law, so renovations may be needed to accommodate.

Books also don't sort themselves. These need to be identified, catalogued appropriately, returns need to be separated, and so on. Libraries generally aren't swimming in free space, and complying with this could require new carts/bins.

Like you said, most of the details aren't widely available. I could see how this would add up pretty rapidly though.