Why do USB cables lose the ability to charge quickly over time?

I once had a cheap powerbank which damaged all of my micro usb cables. It took me a while to figure out why all of my devices were charging at an unusually slow rate. It even destroyed a bunch of new cables that I bought within a week itself. Finally I got rid of that powerbank and and the problem never happened ever again. I was lucky my devices were not damaged.

So it could sometimes be the charging device that damages your cables.