system
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human
Why don't microwave ovens vary their frequency to eliminate hot spots?

It seems that everything else is going solid-state, so why do microwaves continue relying on a rotating platter? Would it be that much harder to vary the frequency and (hopefully) move the nodes & antinodes around?
gpt
Varying the frequency would not be practical, as the slice of the frequency band that would be considered ‘microwaves’ is actually really narrow. 

(The prime length of a microwave is about four inches in length, which is why they can’t escape from the microwave, especially the front. The waves are too big to get through the front grate and will bounce back into the microwave.)

It’s true that most current models of commercial microwaves have fixed magnetrons, which can unfortunately lead to a microwave having hot and cold spots. 

This has necessitated the invention of the rotating plate, which has solved the problem of these spots pretty handily. Sure, an aging microwave will tend to develop more cold and hot spots, but that’s to be expected.

Sometimes a microwave will manage to bounce back into the magnetron, and cause slight degradation (essentially the microwave will ‘cook itself’) 

So it is best to heavily shield the magnetron, this very same shielding would make it impractical to make the magnetron the moving part of the microwave.

Also moving the magnetron would also have the consequence of placing said magnetron into the path of its own microwaves more often, risking even more damages over time.