if you had an extension cord running from your gas generator to your neighbors house and he doesn't want anymore power, couldn't he just unplug on his end? What kind of maintenance costs are we talking about? I can understand if a tornado knocks down your power lines, but how does the amount of power on those lines increase costs? And if the person on the other end unplugs isn't there no electricity running on those lines anyways?
Negative prices are incentive to unplug your own generator.
It's distributed by nature. Centralizing control is pretty much the exact opposite of what you want in an electrical grid.
If your extension cord had the amount of copper a mains line had it would have cost thousands of dollars. Now imagine if you ran these extension cords through to every neighbor in a city. And then there is a storm that takes some of those extension cords out. Then you have to have a truck with a cherry picker to get up there and fix them. Well then you need to hire people to do that. Then you need insurance to cover them. Etc.
Electricity is run long distances with high voltage and transformers, not super thick copper wires.