They only need to measure the current in the live (or lives). The neutral current is not needed. If you open a meter, the middle two terminals are just a block with a tiny little connection for voltage measurement. In fact, on older installs, where the meter was remote, it was common to run two full sized lives and a single smaller neutral. Not done these days. 11,000v metering is done with VT meters reducing the voltages to 110v, but as 11,000v is delta, only two phase need to be connected, the third can be calculated by the meter.