For a lot of companies that’s not even an option; salary levels are fixed. At least at my company, there is a very specific salary range per position. They don’t go below this range even if an applicant requests a salary below the range.

And you’re assuming it’s a conscious bias; it’s not. People will literally view a male as more qualified than an equally-qualified female. They don’t think to themselves “well I could hire this equally-qualified person at a lower salary and save money.” They don’t think of her as equally-qualified.

Of course this isn’t the only reason for the wage gap, but it’s just as silly to say it doesn’t happen as it is to say it’s the only reason.