Because there's a million immigrants from Third and Second world countries competing for that same "trash" min wage job you're trying to get. And they will work for even less. Therefore employers can afford to be super picky and decline people left and right.
You have to rely on nepotistic connections otherwise you're screwed
That may be the case in the US but here in Ireland immigration is tightly controlled. Many asylum seekers are denied the right to work (if at all). You can't just waltz across the Irish border because you'd have to swim through the sea..lol
I think the reason tbh is that people are retiring late meaning older people are competing with younger people for mcdonald jobs.
The internet means that any jobs available on the first page of a job hunting site will have 100s of applicants each more qualified than me.