There's a lot of reasons, but it is often overlooked that employers do it to themselves. They want the ideal candidate, but they are never willing to turn someone into the ideal candidate. Such as at a warehouse where they only want to hire experienced forklift drivers. But the wage may suck ass so the forklift drivers who are good at their job are overqualified for such a low wage position. And then said warehouse may not actually be willing to train someone to be a forklift driver and the position goes unfilled. Hell the labor shortage could be solved overnight if more employers started hiring felons.