> How is a whole demographic group not qualified for jobs on wide spectrum?

If a demographic groups has, for example, a culture that encourages overconfidence in relation to actual qualifications, then it is reasonable to expect that that demographic group will be relatively over-represented in the application pool relative to its aggregate qualifications.

Similarly, a culture that instills under-confidence relative to actual qualifications can be reasonably expected to be under-represented relative to its aggregate qualification.