I've come across a few of these, and at first suspected cats or dogs chewing/clawing on them and or too much exposure to direct sunlight etc.
It soon dawned the cable sheath/covering is literally flimsy, flakey crap, depending on which back alley 'HowLoKanUgO' factory churned it out for Apple Co.,
though in their defense I have also come across some that appear identical yet are top notch quality
Usually if the wires are ok, I first I give it a good once over wrap around with good quality white electrical tape that won't goo when heat is applied,
then do one continuous (or partial) cover all with either white or clear heatshrink, and offer no apologies for the appearance and stiff handling.
They work great, and $5 worth of tape and heatshrink is a better deal IMO than a new charger
whose internals may be worse than the previous batches ...that Apple should HEAVILY discount or offer changeover rates for verified Mac owners who submit their knackered/faulty ones