The answer to 'why is my garbage disposal frozen' is that the disposal is likely jammed or frozen due to a buildup of food waste or debris. This can happen if you've put something down the disposal that it couldn't properly grind up, or if you haven't been running it regularly to clear out waste.
Common signs of a frozen garbage disposal include a humming sound when you try to turn it on, or the blades not spinning freely when you manually rotate the disposal. If the disposal is completely frozen, you won't be able to turn it on at all.