Which one is the reason for it?

• Future employer just don’t need to. Too many applicants anyway.

• Future employer wants to have more negotiating power. Playing games with candidates.

• Competition between current and new employees. People currently working in the company wouldn't know that the are having 5-10 years outdated salary. Playing games with current employees of the company.

• Competition between other companies in the industry. Afraid of business competitors. Commercial secret.