Adding a bit of energy to a telegraph line that normally carries a few watts of power is noticeable. Adding the same amount of energy to a power line that carries hundreds of megawatts would be quite a bit less noticeable.
Setting telegraph recorders on fire and melting the circuit platinum contacts wasn’t exactly a minor event. Enough voltage was induced to run cross-country lines and relay stations with the batteries disconnected.
Applying a DC bias voltage to modern AC equipment in distribution runs, having a neutral with an earth connection, will pose an issue.