For two reasons. First, I was expecting the smart devices that could engage in a power management protocol like this would be aware of their own power consumption, and be making requests for power from the power distribution system.

Detection of actual current consumed (in case they report incorrect numbers or are dumb devices) is more appropriately done on the per circuit basis, and inside the power distribution panel where the circuit breakers are. In fact, what would make sense is a smart circuit breaker which actually measures the current flowing through it and reports it somehow.

One guy I know has built a complete power control system for his house by putting inductive rings (sub-$1) around all the conductors coming out of the circuit breakers. These are connected to a multichannel A to D box so his computer can read current at any time through any circuit. He leared a lot about all the power consumption in his house and is productizing it. (You can also sense current using the hall effect, but I think that's more expensive than using a core when you know you are dealing with 60hz sine wave AC.)

Today a typical fridge uses several circuits, with dedicated ones for oven, microwave, appliances and often fridge. One could certainly imagine a system using fewer circuits because the fridge simply avoids turning on the compressor while the microwave is going, or the coils in the oven only heat while the fridge compressor doesn't run etc. This is not about measuring current, actually. If the devices make a mistake and draw too much current, the breaker blows, as always.