IIRC it has something to do with tubers also being the part of the plant that is used as food[0]. Why is that considered an exception while something cinnamon, where the bark of the plant is eaten and also used in asexual propagation, is not? No clue. Really most of this boils down to "because the law says so" or "because the courts said the law says so."
I'm going to guess it has something to do with the process before the product reaches you.
If you buy a potato, it, on its own, will reproduce given the right circumstances. You can grow an apple seed, too, though that apple seed isn't likely to grow the same apple. You might get something out of an onion, though it is hard to grow a garden full of them without some work gathering seeds and so on.
You an patent certain types of apples, though, and the trees (though not so much what comes from seeds): Eating apples are generally clones. Getting a nice, sweet apple is a lucky thing - Johnny appleseed was realistically spreading cider apples and/or what we would call a crabapple now. In addition, many purchased apple trees are grafted onto different roots to make them more robust.
Similar thing with cinnamon. I've never seen fresh cinnamon bark for sale in a spice isle, just like I've never seen an apple branch for sale. Nor rootstock that wasn't an edible plant. Cinnamon bark is, at best, sold dried - and depending on the variety, it isn't even the entire bark, but just the inner layer. This isn't really what folks use to cultivate cinnamon, by the way [1], and i'm guessing that a lot of cinnamon patents are more geared towards extracting oils and drying/harvest methods.
