[bunderbunder]

It's not just about constancy, it's about having some relationship between how much you pay and how much you use. Utilities that offer that "pay the same every month" feature base the amount you pay on your average usage throughout the year.

Here's an analogy that's closer to cell phone unlimited plans: Imagine if it were instead the same flat fee for everyone across the country. I imagine you'd find the family that lives in a small apartment and keeps the house cool in the winter isn't too happy to find out that very little of their gas bill is explained by their own energy usage, and the vast majority of it is paying to heat the mansions of the rich people across town.