> This provides some efficiency for workers, because there are companies out there who hide ranges and then low-ball really hard

There is an element of psychological warfare introduced by having companies provide hard numbers for what they are willing to pay, especially for industries where employees are less empowered than in tech. By making companies provide salary ranges, you're convincing most employees to not suggest pay that is outside of that boundary. People have a bias towards making choices that appear agreeable, even if it means choosing something like less pay. It's very profitable to convince employees suppress their own pay.