this could be several reasons,
1. after a number of usage, the internal wire at the very end junction of the EarPods may be isolated, damaged or break apart do you to bending and folding during usage.
2. the other reason is also use of max volume could also damage the EarPods, since EarPods work with a vibrating of magnetic coil. as we use high volume, the coils required to jump to the very end of top and bottom of the magnetic field.