Becoming a plumber requires training, which you have to get and pay for yourself. There used to be this place called "community college" which used to give that training at very low (or when I was young, no) cost. Today, even getting into an apprenticeship program requires expenditures.
The call center will hire anyone who's breathing, spend 2 hours training them to not drool on the equipment, and put them on the phones.
Some people don't have the money to pay for technical school. Some people have circumstances that have held them back from being anything more than a minimum-wage call center employee. That doesn't make them ANY less human.
Let me guess. You think people who earn minimum wage LIKE their jobs? Almost none of them do. Almost every one who works for minimum wage is desperate. And it's very difficult to get ahead, if not impossible.
The "free market" has failed us.