@kaia Probably independent power companies started in different states that expanded inwards, without any central planning. They might be using a different frequency or something, or their legislation doesn't make it a public utility like most countries do.
On the plus side, it's harder (slightly) to topple it if there are independent grids, so it might be a cold war thing; they built their cities far from eachother to increase the chance of surviving nuclear bombardment, so it's not off the table that they intended to have one half of the country functioning if the other was destroyed..