Basically, fresh hires have to take calls without appropriate training. Then they make lots of mistakes, or redirect most cases to more experienced colleagues. Because of this, the service level isn't met, and everyone is let off again. Then the cycle starts with new hires, who - surprise - aren't any better.
I worked for a company that was apparently some sort of progressive beacon about 20 years ago. They treated people well, trained them for a month before they took a live call, and even promoted people out.
There was an annual cycle (this business peaked from March-September), but many employees would return and re-qualify. We used to hire 3-4 a quarter as IT techs (out of about 300 agents), and probably about half developed into either IT professionals or went back as call center managers / escalation agents.
Call center work is one, maybe two notches above manual labor. You are (often) sitting at a desk in an (often) air-conditioned office, and your pay is only slightly below median. But it is soul-crushing in ways that manual labor isn't, which can quickly turn into depression.
E: here's a longer article for reference. https://www.google.com/amp/s/www.psychologytoday.com/blog/th...
Basically the next generation of mainframe operators, except with public funding of their vocational training.