>>21584684 (OP)
Because they use volumetric measurements instead of mass. This means you need to be aware of the size/density of your salt to properly convey the quantity required for the recipe. 1 tablespoon of iodized table salt is going to be different than 1 tablespoon of kosher salt.
>>21584730
You just need to weight the teaspoon of salt.
Half of my cookbooks have a table in the beginning detailing the density (volume to mass) of the various ingredients >>21584684 (OP)
Some sort of weird jew worship. They do this even when the salt is dissolved so it's not a texture thing.
iinm, it's just the most common form of non-iodised salt this side of the pond. I use pickling salt to the same effect because it's also non-iodised as well as less than half the price of kosher salt (surprise surprise). Back home, sea salt is more common.