Microwave ovens do indeed have hot spots[0]. Conduction doesn't propagate evenly in very many foodstuffs, and you still want to avoid overheating any one spot.

Microwave ovens do indeed have hot spots[0]. Conduction doesn't propagate evenly in very many foodstuffs, and you still want to avoid overheating any one spot. [0] https://www.evilmadscientist.com/2011/microwave-oven-diagnostics-with-indian-snack-food/