Yeah, I know. But if there was full employment (God, I wish!), they could not afford to be so pathetically choosy and would be glad of any staff they could get.
So, what would happen then? Incompetent staff, who couldn't be bothered to do a decent job or have any incentive to learn since they know there's plenty of other work available. The end product is rubbish and nobody will buy it, so the firm goes broke... Hey, wait a minute, haven't we been here before?
Isn't it obvious that in today's employment environment, employers are going to prefer to employ people with experience? So, what do they do? Hey, I know, let's put in the advert
"Experience required".