Fun fact! EVs use powerline networking for vehicle<->charger communication. Since multiple chargers and cars might share the same circuit (and L2 network), in order to identify the connected car's network endpoint, they've invented a "sounding" protocol to determine the physically closest network node based on signal strength.
Why not distribute ad-hoc networks over powerline / similar constructs? Probably a bandwidth issue. But I’m curious what the specifics are. Take a whole city like NYC? Hmm.
Read ISO 15118 for more details. Here's a paper where they built a sniffer and explore the protocol: https://www.sstic.org/media/SSTIC2019/SSTIC-actes/v2g_inject...