Efficiency of high-voltage power lines
The high voltages used in power distribution are much more hazardous than the 120 or 240 volts we currently have in our homes.  They also require much better (thicker) insulation than lower voltages.

Around here, I think the local high voltage distribution is 12,000 volts.  Most local power distribution here is overhead, so we can see the high voltage lines at the very top of the power poles, on large insulators.  When the power company technicians have to work on the high voltage lines, they keep well away from the lines, using insulated "hot sticks" to manipulate the wires and fittings.  You don't want that sort of voltage wandering aroudn the average home!