/diy/ - Do It Yourself

Because it's safer. Having power lines completely encased in a grounded metal tube greatly reduces the risk of some external element, like a rat, from chewing through the cable and starting a fire.

For context, remember that many homes in America are still ungrounded knob-and-tube. As in, it's just copper hot/return wires soaked in tar going room to room in paralell, offset from boards by ceramic insulators (often broken bits of plates, which was allowed at the time). It was only fully phased out by the mid 1960s, and it was phased out by insurance companies and state inspection boards requiring homes to put all wiring into enclosed pipes.