The cage was originally there to make them more efficient, spraying microwaves into the room would mean you food takes a lot longer to cook.
Anyway, I don’t recall all the details but 1W from a microwave is probably an underestimate.
WiFi uses multiple separate frequencies and outside of what a microwave should be producing. So it’s significantly more energy to block it than you might think especially when the hub is closer to the device than the microwave.
PS: To be clear this is still a trivial amount of energy, just annoying when reheating food blocks WiFi.
