Supply vs demand. But I think you're exaggerating.
When I enlisted around that time it was still a pain center to get enlisted in the Marine Corps. I don't know about the army standards of the time.
But now? They can be picky because the economy is in shambles and people with families need work. In times like WWII you took just about anybody with a pulse because you lost 5k men a day. Now? Not so much.
Sent from my evil, kitten eating cell phone.