What seems to happen is over time moisture causes rust inside the ebrake cables, especially by the rear wheels. Over time it'll rust up nearly solid, but what normally happens is it's rusty enough that you can still apply the park brake with the force of your foot, but rusty enough that the little return springs for the ebrakes can't return the cable.

So if you use the e-brake regularly, any rust that starts up, even just the littlest oxidation, gets rubbed down with regular use and it keeps on working.