My state separates generation from distribution. I literally have a hundred options for generation. I pay a generator to put power on the grid.

I only have one option for distribution. I pay that distributor to convey power (ostensibly) from my generator to my house.

The generator is not the only one with consumption-based costs. The distributor/grid provider also has costs that vary depending on how much power they are moving. They need to upgrade transformers and substations and install additional transmission lines as demand increases. Those have associated costs.

I could understand a flat fee for administrative costs: the power company does have certain per-user costs. But grid maintenance is not one of them: grid maintenance costs depend almost entirely on the total amount of power being moved, not the number of users served. Those maintenance costs are already rolled into consumption. Making them a fixed cost just forces low-use households to subsidize high-use households.