The actual answer is that significant swings in usage create a problem for the utility. It makes capacity planning and budgeting very difficult, and it could even put a strain on the infrastructure, one that isn’t accounted for in the $/kWh.
Like when a youth group shows up st a McDonald’s at 10pm on a Thursday night, and 60 teens each order a box of chicken nuggets. You might think “Oh good, more sales,” but now they are going to run out of nuggets over the weekend. Will they be back next week? Should the restaurant increase staff or stock up on nuggets? What if everyone wants a cheeseburger next week?
Residential energy consumption is predictable. Hidden grow houses are not.