At least in my country the metering is done _in_ the house so my neighbour has to break and enter to tap the line behind the meter. I would probably notice well before bills would pile up. If he taps it outside, probably no one would ever notice if done right. The grid looses energy all the time. Not every kWh that goes into the network is billed in the end.

As always, it just doesn’t make an awful lot of sense to compare physical and virtual worlds. As in leaving your front door unlocked in rural areas vs not securing your remote shell access.