Your definition of how it should work is correct, Quokkas, but employers can't overcome every disadvantage and it can all go very wrong when, for any number of reasons, they still fail to get sufficient applications from those they're keen to attract
That's when some - ignoring the nuances involved - simply cry they're "doing it wrong", and a situation can easily arise where, regardless of merit, they'll appoint anyone they can get in order to get the more unthinking campaigners off their backs
The alternative would be to address, openly and honestly, whatever factors have created the disadvantage, but that could highlight issues which some would find uncomfortable, and which aren't easily resolved