I think the secret salary thing is something employees have been fooled into thinking is something best for them because it's really not at any level good for the employee and that's from the CEO all the way down to the janitor.
Companies like to push this narrative that it's secret and private. I've actually had companies give punitive actions and threaten people if they were going to share their salary with others. There's two reasons companies that don't want you to share your salary with your peers. First is because the companies want to pay you the least amount that you believe you are worth in your job position. The secret salaries allow them to do this quite effectively because you can have two employees that are equal performers but one may understand their value to the company better than the other and negotiate for a higher salary. The company is fully willing to pay the higher salary because they understand the value of the work they're getting but if someone's putting out the same work value but doesn't realize the value that they're bringing they will accept a lower salary and believe it's appropriate.
The second reason companies wanted kept secret is because not everyone's work value is the same even when you're in identical positions. So many HR and management people are so incredibly passive that they cannot just be honest and let employees know that yes you're in the same position but another employee may do 30% more work than you and they can be appropriately compensated for the extra value that they bring. Keeping the salaries secret totally avoids this confrontation and having to defend the different pay levels.
No employee ever gets a benefit from a secret salary. It does not promote honesty it does not promote honest self-assessment. Making salaries known would solve a lot of problems and foster an overall better work environment. If you were at a company and knew that the person in the next chair over that you perceived to be doing the exact same level of work that you were doing but they're receiving 20% higher compensation you could go to your management and ask them why. If you are unsatisfied with the answer you immediately know that this company is undervaluing you and you can seek employment elsewhere for your correct value or you might find out that you have overestimated your work abilities and you need to correct your own self perception.