People need confidence, entitlement, or experience to ask for their worth. Employers know this. Companies brag about taking advantage of information asymmetry to pay us less and we applaud them for it?
It's the same as buying anything brand name, you're paying for the (presumed) higher probability of higher quality or reduced chance of failure.
Transparency of salaries would be a boon to the general public, but we have such a huge social stigma against discussing pay, that employers can take advantage of this, however that's not the employer's fault.