There's a sense that pay transparency will increase competition for lucrative roles and decrease overall comp (but perhaps increase average comp). A lot of people think they have it good and it'll be worse when there's pay transparency (even though this is not true transparency, it's simply public pay bands for listed roles).
Many people are underpaid, but are happy. Telling them they are underpaid and broadcasting it to the world is a great way to destroy that happiness.
This becomes even worst when there are non-monetary benefits to a job (e.g. you highly value working outdoors, beautiful scenery, a fantastic commute).
