Debt is a commodity because people like you exist. As long as there are people who will break their financial obligations there will need to be people to collect from them.

Each company can't always have an internal collection team, because debt collection, especially from people that have no intention of paying it back, is a specialized skill. It makes more sense financially to sell the debt to a collection agency for a fraction of the original value and let them use their specialization to try and more effectively recover the debt.

The core principle here is that when you make a financial arrangement and agree to pay someone something, you need to honour that agreement. If everyone did that we could live in a society where debt was not a commodity. But we never will, because you exist.

And before you even argue that "well then credit just shouldn't be a thing" it most definitely should. Credit is a valuable commodity to have, lets look at the biggest ticket item there is, a mortgage. Unless you are some big wig CEO, and let's face it, you couldn't pay a 200$ cell bill, so your not. You can't possibly afford a house up front. So you can either rent, and never build any equity, just keep paying your landlords bills (oh wait, you didn't do that either). Or you can get a mortgage, and built equity. Its a great example of one of the uses of credit.

What's that you want another example? How about a cell phone then. You pay a monthly fee up front for your base service, you have an agreement with your provider regarding any overage costs and other pay per use features. Now in a world without credit, you would not be able to ever exceed the value of your base plan, so that means if you want to make a long distance call you better know exactly how long you are going to talk for because you will need to do the math to figure out how much extra money you need to pay in advance this month. Or you could be extended credit from the provider for the LD calls and just pay exactly what you owe on the next bill.