Originally Posted by
bent-not-broken
Brake cables and shifter cables are not the same. Brake cables need to be stiffer, typically coil wound so that the don'e compress under the higher load of braking.
Sort of the opposite of that, actually... brake cables can be coil wound because it doesn't matter if they compress a bit. Indexed shift cable housing is compressionless because if it compressed it would throw off the indexing, but can't handle the higher forces that brake cable housing needs to. With friction shifting rather than indexed, coil wound cables can be (and were) used.